Internationa l Journal of Geosciences, 2014, 5, 107-121 Published Online Januar y 2014 (http://www.scirp .org/journal/ijg) http://dx.doi.org/10.4236/ijg.2014.51012 Carbonate Enrichment in Volcanic Debris and Its Relationship with Carbonate Dissolution Signatures of Springs in the Sabga-Bamessing, North West, Cameroon Raymond Beri Verla1,2*, Germain M. M. Mboudou1, Olivier Njoh1, Gilles Nyuyki Ngoran2,3, Aloysius Ngambu Afahnwie1 1Department of Geology, Facult y of science, Un iversity of Buea, Buea, Cameroon 2Explorers 33 Consultants, Yaounde, Cameroon 3Ministry of Min es , Yaounde, Cameroon Email: *verla6@yahoo.com Received October 25, 2013; revis ed November 27, 2013; accepted Dece mber 13, 2013 Copyright © 2014 Raymond Beri Verla et a l. This is an open access article d istributed under the Creative Co mmons Attrib utio n Li- cense, which permits un restricted use, distribution, and reproduction in any medium, provided the original work is properly cited. In accordance of the Creative Commons Attribution License all Copyrights © 2014 are reserved for SCIR P and the o wner of the int el- lectual property Raymond Beri Verla et al. All Copyright © 2014 are guarded by law and by SCIRP as a guardian. ABSTRACT Sabga-Bamessing is a part of the Bamenda Mountains, an extinct volcanic center of the West Cameroon High- lands along the Cameroon Volcanic Line (CVL). The pristine volcanic rocks of the Sabga area are alkali mafic to felsic (basanites, phonolites, trachytes and rhyolites). Some weathered sections of a heterolithologic debris flow with a suppositious primary chemistry of the original volcanic rocks prior to weathering have shown significant calcium carbonate enrichment. CaO and LOI values of up 61.31% and 41.72% respectively show correspo nding enrichment of 16.54 and 10.88, when compared with average fresh volcanic rocks. Na+ normalized molar ratios computed from the chemistry of springs and rivers show carbonate dissolution signature which is contrary to silicate disso lutio n ex pect ed in a cid vo lca nic rocks. Sat ur at ion indi ces (SI) cal culat ed wit h PH REEQC reve al t hat brackish to saline spri ngs are supersatura ted with C alcite (CaCO3) , Aragonite (CaCO3), Dolomite (CaMg(CO3)2 and Hydroxyl apatite (Ca5(PO 4)3OH). Recharging contributions to spring water chemistry deviate from those produced by rock weathering, precipitation and evaporation/crystallization. An enrichment process is therefore predicted as a recharging contributor to water chemistry. KEYWORDS Cameroon Volcanic Line (CVL); Carbonate Enrichment; Carbonate Dissolution; Weathering 1. Introduction The Cameroon Volcanic Line (CVL) is one of the major geological lineaments of the African plate and continent [1]. This N30˚E mag m a t o-tectonic megastructure of Central Africa is a paradigm of active hot lines on Earth made up of continental and oceanic sectors; a unique feature in Africa and even in the world [2]. The Sabga-Bamessing area is a small locality on the west Cameroon highlands an extinct volcanic center of the CVL. Numerous researchers have worked on the CVL and most attention i s directed to wards the genesis, petr ogene- sis and petrology, geochronology, and emplacement me- chanisms of the volcanic rocks [2-7] and other references therein]. The Sabga-Bamessing area conforms to the general geology of the CVL but has certain peculiarities. Explo- sive volcanic activity evident by the presence of exten- sive ignimbrite sheets characterizes the area [8]. Field evidence has shown the brackish to saline nature of water draining certain sections of Sabga. The geochemical as- pects of these fluids have not been fully studied but am- ple evidence shows that the fluids do not reflect the che- mistry of the volcanic rocks. There is an evidence that CaO and Carbonate enrichment has occurred across the profile of a thick and extensive debris flow. The water Corresponding author. OPEN ACCESS IJG
R. B. VERLA ET AL. chemistry of some springs has evolved; bearing a Car- bonate dissolution signature. This paper presents new data showing the peculiarities in ground and surface wa- ter of Sabga due to enrichment and its non conformance to the chemistry of acid volcanic rocks which constitute the main li tholo gy in the are a. 2. Geographical and Geological Context of the Sabga-Bamessing Area The Sabga area is located in the Central African Region in North West Cameroon. The area lies between latitude 6˚00'N - 6˚2'N and longitude 10˚20'E - 10˚22'E. The North West Region of Cameroon falls within the Equatorial climatic domain and precisely influenced by the Cameroon mountain type climate with two seasons; a rainy season from April to October and a dry season from November to March. Annual precipitation and temperature are about 1778 - 2286 mm and 20.5 - 22.3˚C respectively. The vegetation of the study area is generally made of Terminalia trees and shrub savanna derived from moist evergreen forest [9]. The occurrence of bush fires and other a nthro pogen ic activitie s have modifie d the vegetation. The study area equally has a guinea savanna type of vegetation with a mixture of stunted shrubs and grassy undergrowth and has been beneficial for cattle rearing for several decades. The Bamenda country-side also presents a vegetation of raffia palm bush limited to valleys and depressions [10]. Geologically, the Sabga area (Figure 1) is p art of the Bamenda Mountains [11]. It is an extinct volcanic center of the West Cameroon Highlands. This center constitutes a very important part of the continental sector of the Cameroon Volcanic Line and lies mid-way between Bambouto in the south west and the Oku massif in t he north eas t . Figure 1 . Location of the study area w ithin t he CVL; the study are a is sho wn on the satellite image a s a rectangle. OPEN ACCESS IJG
R. B. VERLA ET AL. The Sabga area lies just a few miles (about 15 miles) SE of Big Babanki, one of the stratovolcanoes on the Oku massif. The volcanic rocks range from mafic to fel- sic and include basalts, Mugearites, basanites, trachytes, rhyolites and benmoreites [11-13]. The absolute ages determined for the mafic volcanic rocks range from 10 to 22 Ma from earlier studies; 12 to 27 Ma following recent geochronogical data [11]. The ages determined for the felsic volcanic rocks range from 18.7 - 24.2 Ma for the oldest rocks and 12.7 - 13.2 Ma for the youngest ones. Geochemical studies had previously been done on nearby volcanic centers (Oku and Ndu) and similar geochrono- logic, petrogenetic and petrological conclusions had been drawn [14,15]. The volcanic rocks are emplaced on a granit ic b asement of P an A frican a ge wit h exte nsive out- crops in the Bamessing, and Ndop plains. Field evidence reveals abundant muscovite in the mode of these gra- nites. 3. Sampling and Analytical Procedures Five representative samples from 33 fresh volcanic sam- ples were selected for analysis. Five samples collected from the top and bottom of a weathered volcanic debris flow were equally selected. The samples were oven-dried at 105˚C. Each sample was disaggregated. The resulting chips were put in a porcelain cup together with porcelain balls, cocked tightly and milled for about 30 minutes. The resultant powder measuring about 100 µ or more was put into clean porcelain mortar and using the physi- cal energy, pulverized with a porcelain pestle to finer sizes. A clean 50 µ sieve was used to sieve the pulp ob- taini ng a <50 µ powder. Glass beads and pressed powder discs were made from the powder for major oxide and trace element analyses respectively. A Pioneer S4 Brucker XRF apparatus was used to analyze for major and trace elements in ten samples at MIPROMALO (Mission de Promotion des Matériaux Locaux), Yaounde, Cameroon. Loss on ignition (LOI) was determined by weight difference after ignition at 1000˚C. Twelve water samples (10 springs and 2 river samples) were collected using the conventional methods given in FOREGS geochemical manual [16]; water samples were collected with a syringe which had been rinsed twice with the water sample and put in 500 ml ethylene bottle passing through a filter, followed by the addition of 1.0 ml of conc. HNO3 acid. The samples were shaken tho- roughly and placed in an ice box. Field parameters (pH, EC, TDS, Temp,) were measured for the springs and river samples using pH, EC, TDS meters (Hanna instru- ments, H1 9811) and a digital thermometer. The water samples were analyzed for major cations and anions at the Institute of Agronomic Research and Development (IRAD) in Ekona, SW Region of Cameroon. The concentrations of Na+, K+, and Ca2+, were deter- mined using the Gallemkamp flame photometer. Mg2+, , , , were analyzed by Colori- metry and and Cl − b y titratio n. The major oxides and few trace elements in volcanic materials have been used to characterize the volcanic rocks and compute the enrichment and depletion of ele- ments. Major cations and anions in water are used to do the aqueous speciation calculations to determine satura- tion indic es (SI) using PH R EEQ C [17]. Field data and geochemical data are used together with satellite images to produce geologic maps and models using GLOBAL MAPPER and SURFER 9 software which further highlig ht the spatia l distribution of volcan- ic materials, springs and river s. 4. Resul ts 4.1. Geospatial Distribution of Rock Types A 1:500 geologic map of the study area drawn using combined field and sate llite imagery data with GLOBAL MAPPER 11 and SURFER 9 software reveals that the area has five main rock types, namely, Trachytic, Rhyo- litic, Basaltic, Tuff breccia/pyroclastic breccia, and Vol- canic debris flow (Figure 2). The crystalline rocks are more or less fresh but the debris flow has suffered in- tense chemical weathering. The debris flow has an esti- mated perimeter of 14884.4 m and area of 7175.5 m2. The bulk of the material is a mixture of fresh aphanetic rock frag ments wit h very fine grain friable material in th e ratio 1:3. The overall texture is volcaniclastic and many radial cracks are present qualifying the outcrop as a lahar (Figure 3(a)). Ro unded clayey a ggregat es also consti tute large parts of these outcrops. These sections of the flow are at relatively high topography at about 1650 - 1700 m or more above sea level. The river Nkambie has exposed steep walls about 50 - 60 m high of se ctions of the debris fl ow (Figure s 3(a)-(e)). The wall shows a viscoplastic rheology and abundant sub-rounded boulders at the bottom. The outcrop is pre- dominantly made up of volcaniclastic material. The re- mainder is made up of huge volumes of precipitates oc- curring at the bottom of the exposed wall. A pure white soft precipitate with acicular and feathery habit and a taste peculiar to bicarbonate salts occupies the interstices of the sub rounded boulders (Figure 3(b)). Another dull yellow precipitate with an earthly to massive habit, a sweetish astringent taste and a slight sulphurous odor is also dominant (Figure 3(e)). Most of the samples effer- vesce on the addition o f HCl. This botto m section is rela- tively at lower topography (1450 - 1500 m above sea level). SURFER generated DEM combined with the geolo gic map sho ws that the mai n river ( Nkambie ) flo ws through the base of the debris flow where appreciable OPEN ACCESS IJG
R. B. VERLA ET AL. Figure 2. Geospatial data added on the topographic design (geologic map) both in 2D and 3D for the study area. The main rock types are classified using field classifications [18-22] and other identi fication parameters . OPEN ACCESS IJG
R. B. VERLA ET AL. Figure 3. (a)-(e): Bott om sect ions of a debris flow in Sabga. (a) Outcr ops of volcani c debris fl ow show ing fragments of ro cks in a fine grained matrix that has been weathered. (b) Bottom section of a volcanic debris flow. The upper section above is about 60 m on average. (c) Saline pre cipi t ates on th e bott o m se cti on of the lahar. (d) Basaltic boulders cemented by c arbon ate material. (e) Yellow precipitates occurring with the white precipitates. (f) Evidence of plastic rheology which characterizes debris flow. secondary precipitation and salts have been observed (Figure 2). 4.2. Characterization of Volcanic Rock and Weathered Volcanic Debris The volcanic rocks are geochemically classified on the Harke r diagr am usin g the To tal Alkali ( Na2O + K2O) vs. Silica (SiO2) classification (TAS) [22], as Basanite/ Trachy-basalt, Phonolite, Trachyte/Trachydacite and Rhyolites (Figure 4). SiO2 concentrations range from 47% - 73.31%, while concentrations of Al2O3 ra nge fro m 11.93% - 20.49%. CaO concentrations range from 0.136% - 9.86% and MgO range from 0.103 - 4.55. Na2O and K2O concentrations range from 2.227 - 6.534 and 2.22 - 6.776 re s pec t ively . Incompatible trace elements (LIL, HFSEs), Rb, Nb, Zr, Y, and Zn are pr esent with N b and Zr having the hi ghest frequency of occurrence in the samples. The major o xide chemistry is pr e sented in Table 1. Comparing the major oxide chemistry of volcanic Figure 4. Classification of Sabga volcanic rocks on TAS diagram [22]. OPEN ACCESS IJG
R. B. VERLA ET AL. Table 1. Major oxides, normative mineralogy and trace element concentrations in v olcanic rocks. Sample code B4 BR10 T5 RH1 T25 SiO2 47 73.21 56.98 72.66 67.28 TiO2 3.264 0.316 0.679 0.616 0.389 Al2O3 15.71 1 6.1 20.49 12.02 11.93 Fe2O3t 11.38 0.6869 7.014 2.833 5.811 MnO 0.19 0.0794 0.143 0.01 0.106 MgO 4.551 0.32 0.103 0.35 0.38 CaO 9.86 0.434 0.49 0.136 0.371 Na2O 4.311 2.27 6.534 4.485 6.106 K2O 2.22 4.633 6.075 5.061 6.776 P2O5 0.645 0.041 0.128 SO2 0.116 0.0693 0.0221 0.0334 LOI 0.76 1.89 1.51 1.8 0.69 SUM 100.007 100.0086 100.018 100.0341 100.0004 CIPW NORM Q 40.868 29.058 21.104 C 6.562 2.274 Or 13.12 27.38 35.901 29.909 4 0.044 Ab 30.292 19.208 43.499 33.648 23.637 An 16.958 2.153 2.431 Ne 3.352 6.387 Ns 1.001 6.524 Di 13.326 0.051 Hy 0.797 0.872 0.923 Ol 3.614 0.18 Il 0.406 0.17 0.306 0.021 0.227 Tn 0.287 0.662 Pf 5.193 Ru 0.227 0.518 0.488 Ap 1.528 0.097 0.303 Sum 87.789 97.364 91.496 95.382 93.474 DI 46.764 87.456 85.787 92.618 84.606 Mg# 30.76455 34.1075 1.605462 12.07021 6.773739 Rb 81 190 251 Ba 794 Nb 69 86 424 226 425.9 Sr 969.4 Zr 319 555.6 2139 1017 2864 Y 52 36 88 77 Ga 50 40 49 V 198 Cr 267 Cu 70 Zn 66 363 124 183 Ce 530 rocks of Sabga with some rocks in other parts of the world e.g. comparison of sample B4 and the alkali oli- vine basalt sample KLPA-1, of Molokai volcano, Hawaii [23] and RH1 with Circle Creek rhyolite, sample 60NC145, Nevada [24], has shown almost the same chemistries. No peculiarities are presented by the Sabga volcanic rocks. The Mg number s (Mg# = MgO/MgO + FeO) with Fe O calculated as 0.9Fe2O3t range from 1.605% - 30.765% with an average of 17.064. Norms are computed from the major oxides using CIPW normative mineral calculations [25,26], giving hypothetical mineral phases that might be present in the volcanic rocks. Differentiation index (DI) calculated from norms as the sum of Q+ Or + Ab+ Ne [27] show that DI range from 46.764 - 92.6 with an average of 79.44. Normative minerals include quartz, corundum, orthoclase, albite, anorthite, nepheline, nos ea n, di opside, hypes t hene, olivine, ilmenite, titanite, perovskite, rutile and apatite (Table 1). Normative quartz, orthoclase and albite dominate mean- while normative anorthite is in lesser percentages. Other mineral phases containing CaO such as Diopside, Hyper- sthene, perovskite, and titanite occur in very small con- centrations. Weathered volcanic material and secondary precipi- tates all parts of a single volcanic debris flow produce major o xides essentially similar to the oxides in the fresh volcanic rocks (Table 2). The concentrations of the oxides vary especially in the precipitates but the wea- thered materials at higher topography (CL1) have SiO2 and Al2O3 concentrations of 70.01% and 11.3% and these are similar with those of the fresh rhyolite (RH1). K2O concentrations are equally similar but there is a marked reduction of about 92.7% in the concentration of Na2O. Ash and precipitates at the base of the volcanic debris have very high concentrations of CaO (32.4% av- erage), SO2 (11.5 %) a nd ver y lo w conc entr atio ns o f S iO2 (17.91% average), though the base ash (ASH B) has a SiO2 concentration of 60.3% similar to that of fresh in- termediate trachytic rocks. CaO concentrations in some of the precipitates (SIL, SAL1) are higher than those commonly found in limestones. Fe2O3t and SO2 are high (16.13 and 45.99 respective- ly). These precipitates and bottom volcanic ash are also characterized by high losses on ignition of average 25.9%. 4.3. Estimating Element Losses and Gains from Fresh and Wea thered Volcanic Ma ter ial s The lahar (Figure 3) has been studied as a zone of in- tense weathering and leaching of material. To estimate major losses and gains in elemental concentrations, an enrichment and depletion diagram (Figure 5) is used. The following assumptions are made in the calculation: The volcanic debris is considered as heterolithologic consisting of all the primary rock types present in the area. OPEN ACCESS IJG
R. B. VERLA ET AL. Table 2. Major oxides and trace element concentrations in weathered v ol canic materials and secondary preci pitates. CL1 SIL SAL1 SAL 3Y ASH B SiO2 70.01 1.51 3.68 6.11 60.34 TiO2 0.272 0.023 0.49 0.27 0.675 Al2O3 11.3 0.314 1.2 2.17 5.733 Fe2O3t 3.884 0.253 4.235 16.13 5.244 MnO 0.0557 0.165 0.121 0.0697 0.194 MgO 0.652 0.403 CaO 0.473 54.7 61.31 6.894 6.842 Na2O 0.328 0.472 3.28 K2O 5.971 0.136 0.775 2.076 3.675 P2O5 0.015 0.13 0.19 0.0928 SO2 0.042 0.05 0.128 45.99 0.013 LOI 7.7 41.72 27.94 20.11 13.54 SUM 100.0357 100.01 100.009 100.0097 100.0318 Rb 1055 70 Nb 202 30 Sr 835.7 267 40 130 Zr 1255 14 204 92 208 Y 235 Ga 50 Zn 349 120 70 99 La 560 0 Tb 55 Figure 5. Enrichment depletion diagram for average com- positions of fresh and weathered volcanic rocks/precipi- tates. The average composition of all the fresh rock types is considered as the original debris irrespective of the grain size. The material at the top of the lahar, though weathered is considered together with the fresh rocks because of its chemical similarity with rhyolites. The average chemistry of all the material at the bot- tom of the debris flow is calcu la te d. The difference in magnitude when the two sets of averages (major and trace elements) are considered as ratios is calculated as the depletion (negative) or as enrichment (positive). CaO is seen to have been enriched up to 16.54 times its original average value of about 1.96 while LOI has been enriched 10.88 its original average value (2.37). Fe2O3t, MnO, and Sr have also been enriched at the base of the lahar but in le sser amounts (Figure 5). High loss on ignition is related to high carbonate, bi- carbonate and sulphate ions associated with secondary precipita tion at the botto m of the lahar. 4.4. Hydrochemistry of Springs and Rivers The hydrochemical data (Table 3) reveal that the domi- nant major cation is Ca2+, followed by K+ for the brack- ish-saline water springs and rivers. Mg2+ dominates as second main cation for the fresh water springs. The anions are in the order > > Cl− for the brackish-saline water springs and > Cl− > for the fresh water springs and rivers. The total cations (TZ+) and total anions (TZ−) range from 20.09 - 917.72 mg/l and 20.83 - 12,292.32 mg/l respectively, resulting in averages of 251.87 and 2971.9 mg/l. Ca2+ constitutes on average 65.21%, of the total cations in meq/l while Mg2+ and Na+ + K+ contribute 21.33% and 13.45% respec- tively. constitutes averagely 76.75% of the total anions in meq/l while Cl and SO4= contribute 19.26% and 3.98% respectively. Anomalous concentrations especial- ly of Ca2+, K+, and are associated with springs labeled SP1, SP2A, SP7, W1 and W2. The per- centage of Ca2+ increases further to an average of 71.55% and to an average of 92.16% in the highly con- centrated springs. There is a great variation between the cations and anions. Resulting in negative ion balances (–65 to –92.2) in the highly bicarbonate concentrated springs. TDS as high as 5188.8 - 11,570.2 mg/l classify the highly concentrated spring water as brackish to saline [28]. Piper diagram (Figure 6) places the water into Ca + Mg-HCO3 + CO3 a nd HCO3 + CO 3 hydrochemical facies [29]. The water from both the rivers and the springs straddle the Ca- Mg apex of the major cation triangular plot in Figure 6. This shows the presence of an important Ca2+ and Mg2+ source in the area. This signature is dif- ferent from t hose of spr ings al ong the CV L with Na+ and K+ signatures interacting with almost the same rocks (in- termediate-ac i d) l ike t ho se found in S ab ga . This mig ht be signifying another origin other than the intense water- silicate-rich rock interaction [30] we will expect in areas with acid rich rocks; where the major cations generally cluster around the Na+ and K+ apex of triangular plots. Na+ normalized molar ratios [31] are calculated and presented in Table 4 and summarized in Figure 7. It should be noted that these values for rivers were not cor- OPEN ACCESS IJG
R. B. VERLA ET AL. Table 3 . Sa mple l ocation p oints, summary of the hydroche mistry and field parameters (EC, TDS, pH, Temp) of springs (1st ten) and rivers (last three) . Long. Lat Na+ (mg/l) K+ Ca2+ Mg2+ Cl− HCO3− NO3 NH4+ TZ+ TZ- IB EC (µ s/ cm) TDS (mg/l) pH Temp (˚C) SP1 10.34118 6.03052 1518 6.9 2 60 .45 8.51 8 4782 82.13 0.67 0.1 565 .99 4954.93 −69.3 7744.5 5188.8 7.1 20 .3 SP2A 10.3481 6.02177 1389 5 .91 44 .07 4.97 24 3050 64.64 0.1 3 0.06 430 .72 3203.41 −65 5043.3 3379 7.4 22 .1 SP2 10.34824 6.02185 1389 0.4 1 5.46 18.6 6.54 8 43 1.79 0.02 0.79 56 .15 54 .6 2 5 .3 125 .1 83 .8 7.2 21 SP3 10.34981 6.01488 1322 0.2 1 2.73 11.2 6.75 9 20 0.48 0.97 0.0 8 38 .84 29.96 33.7 75 .2 50.4 8 24.2 SP4 10.33232 6.02016 1680 0.2 1 2.34 7.4 4.78 12 29 0.02 0.13 26 .91 41 .02 1.1 83 .1 55.7 6 .4 20 .6 SP6 10.32604 6.021451 1657 0.23 3.51 11.2 0.57 9 23 0.21 0.24 27 .28 32 .42 5.2 71 .2 47.7 6 .8 18 .9 SP7 10.33678 6.02327 1477 7.9 8 65 .52 27.8 8.3 2 12 6015 72.49 0.0 9 1.29 145 .74 6172.07 −92.2 9267.3 6209.1 7.7 19 .7 SP8 10.33752 6.030219 1604 0.23 3.12 14.8 6.75 5 41 2.13 0.47 0.48 46.45 50.73 23 .5 108 .9 73 7.9 20 .1 W2 10 .33893 6.02003 1457 13.25 97.89 32.69 9248 1064.26 0.34 2.4 1 917 .72 11532.5 −76 16392.1 10982.7 8.6 23 .3 W1 10 .33809 6.02029 1449 13.25 96.72 14.24 9675 1216.39 0.56 1.37 879 .65 12292.3 −78.6 17269.0 11570.2 7.87 21.6 ST1 10.34108 6.01915 1459 0.8 5 7.8 33.4 8.1 5 9 201 6.2 0.71 1.26 0.1 2 91 .75 223.11 −17.7 397.6 266.4 7 .6 18.9 RNK1 10.34111 6.02419 1446 0.2 5 2.34 11.2 1.07 6 12 0.9 1.03 27.13 20.83 30 .2 5 0 .4 33.8 7 .6 18 .1 RNK2 10.32582 6.021451 1663 0.12 1.95 7.4 1.61 5 22 0.98 0.24 20.09 27.98 5 .2 56 .8 38.1 8 .6 1 8 .4 Table 4. Na+ normalized molar ratios for Sabga spring and rive r water. K+/Na Ca+/ Na Mg+/Na H CO3/Na SO4/Na Cl−/Na SP1 5.136324 19.96005 1.162994 259.9827 2.840482 0.749733 SP2A 4.384477 17. 99424 0.795285 194.1571 2.617642 2.63358 SP2 7.830167 26.02198 15.08509 39.45713 1.044878 12.65403 SP3 7.643734 30.59215 30.39754 35.8304 0.547039 27.79367 SP4 6.551772 20.21267 21.52596 51.95407 37.05823 SP6 8.973079 27.93196 2.343695 37.62192 0.218518 25.37683 SP7 4.827621 1.998265 0.985994 283.5787 2.17406 0.975217 SP8 7.97607 36.91009 27.75428 67.06515 2.2164 14.09824 W2 4.343948 16.04356 2.333206 262.5868 19.22331 7 .635394 W1 4.292029 16.04356 1.016361 274.711 21.97118 9.005849 ST1 5.395577 22.53922 9.067607 88.96476 1.745698 6.866672 RNK1 5.503488 25.69741 4.047602 18. 05852 0.861587 15.56446 RNK2 9.554668 35.37217 12.68816 68. 97351 27.02163 rected for atmospheric inputs because of the negligible concentrations in rain water. Average values for Ca/Na, Mg/Na, HCO3/Na, and Ca/Mg molar ratios are 22.87, 9.94, 129.5 and 7.5 respectively. These values are several magnitudes higher than the high values [31] for riv- ers/water draining basalts (Ca/Na: 0.2 - 3.15, HCO3/Na: 1 - 10, Mg/Na: 0.15 - 3.15), though the Mg/Na for the HCO3-concentrated springs reflect those for water drain- ing basalts (Mg2+/Na: 0.15 - 3.15). The Na+ normalized plots show a trend which gener- ally shifts towards and occupy the carbonate dissolution end and a general shift away from Na+ (Figure 8). In comparison with the diagrams in [31], the springs with anomalously very high bicarbonates lie above the carbo- nate dissolution zone and can be considered as zones of bicarbonate concentration. It is also evident that these springs are less concentrated in Mg2+ relative to the other spri ngs a nd ri vers a nd have Mg+/Na+ mola r val ues withi n the range for water draining basalts. Na+ normalized mo- lar ratio trends for the brackish-saline springs (Figure 9) sho w a gradual concentration of springs down slope rela- tive to their sampling point elevation. The brackish-saline springs are supersaturated with certain mineral phases: SI of Aragonite (0.8 - 2.61), cal- cite (0.96 - 2.86), dolomite (1.7 - 5.0), and hydroxyl apatite (0.16 - 8.62). Mineral saturation is presented in OPEN ACCESS IJG
R. B. VERLA ET AL. Figure 6 . Piper diagra ms for the Sabga spring/ river water samples showing the major hydrochemical facies after [29]. Figure 7 . H istogram showing the Na normalized molar ratios for the spring and river w at er samples. Figure 8 . Na normaliz ed molar rat io plots [31] f or th e spr ing and riv er w at er sa mple s s how ing the i mpo rta nt c ontr ibut io n of carbonat e dissolution in modi fy ing the che mistry of the springs and river s. Total Dissolved Solids (Parts Per Million) 0.0 20,000.0 40,000.0 60,000.0 80,000.0 100,000.0 OPEN ACCESS IJG
R. B. VERLA ET AL. Figure 9 . Conc e ntr a ti o n tr en d for the brac kis h/ sa line spr i ng samples down gradient. Table 5. The abundance of calcium oxide phases in the minerals is indicative of the dissolution of calcium car- bonate rocks. Plot of TDS vs Na+/Na+ + Ca2+ (Figure 10) show a deviation of spring water samples from the three re- charging contributions postulated for spring water che- mistry [32]. Such a deviation supports one of the major outlined short comings [33] with the diagram, that there is no place for waters which have been affected by do- mestic contamination or other sources of hydrochemical enrichment outside of the three proposed sources. 4.5. GIS/Hydrogeologic Models The concentrations of major ions considered as third coordinate axes are plotted in 3D, on the same longitude and latitude space (first two coordinates) used in gene- rating the 3D topographic model and stacked on the later (Figure 11). The highest concentrations coincide with a geomorphic structure; a shallow volcanic maar. 5. Discussion The geologic field mapping presents a volcanic area with volcanic domes and plugs characteristic of acid volcanism. The satellite image (Figure 1) confirms that the area is characterized by explosive volcanic activity due to the presence of the Foleshelle cr ater. The rock types are gen- erally acid rocks with the trachytic rocks comprising about 34%, rhyolitic about 24% and tuff breccia and ba- saltic r ocks making 15% and 7 % respec tively. The north- ern slope of the area is made up of volcanic debris flow (lahar) mater ial making up to 29% of the study area and is evidence of the explosive and strongly aci di c nature of the Sabga lithologies [8]. The rock types studied are consis- tent with names mentioned [11,13] for r ocks occurring in the Bamenda Mountains and also for those [14] in ne arby Oku and Ndu. The trachytic plug, together with rhyolitic and basaltic outcrops present very little weathering (chemical decomposition) meanwhile the massive vol- canic debris flow (lahar) has been weathered. Field stu- Figure 10. TDS vs. Na+/Na+ + Ca2+ plot [32] of springs in the Sabg a -Bamessing and environs. dies also show that the debris is relatively weak as com- pared to the other rock types from the deep river valleys cut through by the Nkambie River (F igur es 2 and 10). Where the river has been cut so deep, carbonates and salts are seen to precipitate from fluids seeping at the bottom of the debris. The saline springs (highly concen- trated bicarbonate springs) are associated with very shal- low circular marshy depressions and breccia (SP7, SP2A, W1, and W2) or occur and have an intimate connection with the bottom of the debris flow (SP1). Using spatial distribution of rock types and normative mineralogy, albite and orthoclase are dominant and by theory should dominate in the water chemistry. The dominance will be reflected in spring and river water draining this area as Na+ and K+ when considering the acid nat ure of the vol- canic rocks. The dominance of K+ and Na + has been stu- died in many fluids draining acid and intermediate rocks along the CVL [30]. The water chemistry has evolved showing a chemistry dominated by Ca2+ and . This evolved chemistry closely is consistent with the chemistry of the weathered materials and precipitates (high CaO and LOI) at the bottom of the debris flow. The carbonate character of some springs such as the Fossette spring along the CVL has been linked to the decomposi- tion of volca nic ash [3 4] . In S ab ga the re gio n enr iche d i n secondary carbonates might be a result of prolonged chemical weathering, resulting in element leaching and concentration. results exclusively from wea- thering [31]. High concentrations of in water result in concentration or enrichment of Ca2+ [35]. Al- though enriched, the same elements found in fresh vol- canic rocks are represented in the enriched lithologies and sa line pr ecip itates i n var ying amou nts sup por ting th e idea of source rock isochemical dissolution [36] . The Na+ normalized molar ratio plots showing carbonate dissolu- tion signature is a clear indication of a proximal calcium carbonate mineral source. This is further supported by the high SI values for Calcite, Aragonite and Dolomite computed using aqueous speciation calculations [17]. An enrichment process is therefore envisaged as a rechargin g OPEN ACCESS IJG
R. B. VERLA ET AL. Table 5. S a turat ion i ndices for mineral p hases in the Sabga spring a nd river water c omputed using PHREE QC. Samples Phases SP1 SP2A SP2 SP3 SP4 SP6 SP7 SP8 W2 W1 ST1 RN K1 R N K2 Anhydrite CaSO4 SI −1.81 −1.93 −3.93 −4.68 / −5.01 −2.83 −3.94 −1.03 −0.84 −3.23 −4.38 / log IAP −6.16 −6.28 −8.28 −9.04 / −9.35 −7.18 −8.29 −5.38 −5.18 −7.57 −8.72 / log KT −4.34 −4.35 −4.3 5 −4.3 6 / −4.34 −4.34 −4.34 −4.35 −4.35 −4.34 −4.34 / Aragonite CaCO3 SI 1.09 1.21 −1.51 −1.1 5 −3.08 −2.48 0.8 −0.9 2.68 2.1 −0.24 −1.86 −0.76 log IAP −7.22 −7.11 −9.82 −9.48 −11.39 −10.78 −7.49 −9.2 −5 .6 5 −6.21 −8.54 −10.16 −9.06 log KT −8.31 −8.32 −8.3 1 −8.3 3 −8.31 −8.3 −8.3 −8.3 1 −8.33 −8.32 −8.45 −8.3 −8.3 Calci te CaCO3 SI 1.24 1.35 −1.36 −1.0 1 −2.93 −2.33 0.96 −0.75 2.82 2.25 −0.09 −1.71 −0.61 log IAP −7.22 −7.11 −9.82 −9.48 −11.39 −10.78 −7.49 −9.2 −5 .6 5 −6.21 −8.54 −10.16 −9.06 log KT −8.45 −8.46 −8.4 6 −8.4 7 −8.46 −8.45 −8.45 −8.45 −8.47 −8.46 −8.45 −8.44 −8.45 CO2 (g) SI −0.56 −1.01 −2.64 −3.7 −2.23 −2.6 −1.02 −3.32 −1.75 −1 −2.36 −3.57 −4.29 log IAP −1.98 −2.44 −4.06 −5.16 −3.64 −3.99 −2.42 −4.73 −3.2 −2 .4 2 −3.75 −4.95 −5.68 log KT −1.41 −1.43 −1.4 2 −1.4 6 −1.41 −1.39 −1.4 −1.14 −1.45 −1.43 −1.39 −1.38 −1.39 Dolomite CaMg(CO3)2 SI 1.32 1.46 −2.89 −1.9 −5.77 −5.69 1.7 −1.55 5 3.41 −0.53 −4 .1 −1.62 log IAP −15.66 −15.56 −19.8 −18.97 −22.75 −22.63 −15.27 −18.53 −12.05 −13.6 −17.48 −21.12 −18.55 log KT −16.98 −17.02 −17 −17.07 −16.99 −16.95 −16.96 −16.97 −17.05 −17.01 −16.95 −16.93 −16.93 Gypsum CaSO4:2H2O SI −1.58 −1.7 −3.7 −4.46 / −4.77 −2.6 −3.71 −0.81 −0.61 −2.99 −4.14 / log IAP −6.16 −6.28 −8.28 −9.04 / −9.35 −7.18 −88.29 −5.39 −5.19 −7.57 −8.72 / log KT −4.58 −4.58 −4.5 8 −4.5 8 / −4.58 −4.58 −4.58 −4.58 −4.58 −4.58 −4.58 / H2 (g) SI −22.2 −22.8 −22.4 −24 −20.8 −21.6 −23.4 −23.8 −25.2 −23.74 −23.2 −23.2 −25.2 log IAP −25.33 −25.94 −25.5 −27.15 −23.93 −24.72 −26.53 −26.93 −28.34 −26.88 −26.32 −26.32 −28.32 log KT −3.13 −3.14 −3.1 3 −3.1 5 −3.13 −3.12 −3.13 −3.13 −3.14 −3.14 −3.12 −3.12 −3.12 H2O (g) SI −1.63 −1.59 −1.61 −1.53 −1.63 −1.67 −1.65 −1.64 −1.56 −1.6 −1.67 −1.69 −1.68 log IAP 0 0 0 0 0 0 0 0 0 0 0 0 0 log KT 1.63 1.59 1.61 1.53 1.63 1.67 −1.65 1.64 1.56 1.6 1.67 1.69 1.68 Halite NaCl SI −8.91 −8.49 −10.0 −10.25 −10.11 −10.19 −8.69 −10.46 −7.44 −7.35 −9.66 −10.33 −10.73 log IAP −7.34 −6.91 −8.44 −8.67 −8.54 −8.62 −7.12 −8.89 −5.86 −5.78 −8.09 −8.76 −9.16 log KT 1.57 1.58 1.57 1.58 1.57 1.57 1.57 1.57 1.58 1.57 1.57 1.57 1.57 Hydroxylapatite Ca5(PO4)3OH SI −0.6 0.16 −0.32 −0 .2 8 −9.24 −5.15 0.71 / 8.62 5.65 −0.11 / / log IAP −3.6 −3 −3.38 −3.6 3 −12.27 −8.02 −2.23 / 5.35 2.53 −2.98 / / log KT −3 −3.16 −3.06 −3 .34 −3.02 −2.87 −2.94 / −3.27 −3.12 −2.87 / / O2 (g) SI −40.41 −38.58 −39.7 −35.49 −43.1 −42.1 −38.22 −37.28 −33.37 −36.88 −38.9 −39.18 −35.08 log IAP −43.26 −41.45 −42.6 −38.38 −45.96 −44.94 −41.07 −40.13 −36.25 −39.74 −41.74 −42.02 −37.92 log KT −2.86 −2.87 −2.8 6 −2.8 9 −2.86 −2.85 −2.85 −2.86 −2.88 −3.87 −2.85 −2.84 −2.84 NH3 (g) SI / / / −7.26 / / / −7.87 −7.32 / −7.81 / −7.59 log IAP / / / −5 .4 7 / / / −6 −5.52 / −5.92 / −5.69 log KT / / / 1.79 / / / 1.87 1.8 / 1.9 / 1.91 OPEN ACCESS IJG
R. B. VERLA ET AL. Figure 1 1. Major ion conc entration stacked on 3D topog raphic des ign revealing the region of ion anomaly . OPEN ACCESS IJG
R. B. VERLA ET AL. contributor to water chemistry due a deviation from normal on the Gibbs diagram [32]. GIS and hydrogeologic models have contrib uted enormously in the present study and these are quoted amongst the best tools available used to characterize the environment [37-39]. The regenerated Digital Terrain Model (DTM) presents a real world object which is one of the objectives of 3D GIS [37]. Geospatial data on both 2D and 3D presentation reveals a true picture of the study area. The 3D representation brings a real picture where friable, porous volcanic debris flow material is weathered and the route of resultant chemical load can be hypothesized as being vertical. Groundwater flow vectors produced on the DTM show that the vectors are sub ver- tical to vertical and the ions must have followed the same pathway. The portion shown to be occupied by the vol- canic debris flow extends on the slopes from about con- tour 1380 m to > 1720 m above sea level. Sections of the debris flow cut by the Nkambie River expose heights of about 90 m on average. Thickness in synergy with spe- cial lithology, weathering and removal of chemical load in vertical- sub vertical pathway across the entire profile of a volcanic debris flow might have led to a modified chemistry which is capable of precipitating salts. Sec- ondary carbonate deposits precipitated at about contour 1550 m are considered a point source for the high con- centrations of Ca2+, K+, Na+, , and in some springs in the Sabga area. Adjacent to the volcanic debris flow, the crystalline volcanic rocks are more in an intact stage and have un- dergone very little chemical weathering. It would rather be erroneous visualizing such a high input of salt- for m- ing ions to resul t from these rocks. The topographic model with geospatial data added also sho w how d eep the ri ver N kamb ie has dug i nto the co un- try rock. The ease of vertical erosion and the resultant steep and deep river valleys penetrate the zones of car- bonate concentration and salt precipitation. The river thus acquires the carbonate-bicarbonate signatures also presented by the springs. Hydrogeologic models defining the zone of anomaly for groundwater concentration show highest concentra- tion at low top ographic levels away fr om a hi gh elevation source. The expected fate of the ions will be that ions disperse and loose their salinity unless another process causes them to concentrate. The presence of a rim of tuff breccia surrounding a shallow depression as shown in the topographic and geologic maps both in 2D and 3D supports the presence of a maar. The peak in groundwater ion concentration coincides wit h this local explo sion structure. 6. Conclusions As op p o sed t o the che mistr y of fluids in parts of the CVL interacting with acid to intermediate volcanic rocks, the Sabga fluids (springs and rivers) have adopted a carbo- nate dissolution signature. Carbonate enrichment at the base of a volcanic debris flow is in line with the carbo- nate signature s adopted b y the fluids. H igh salinity (TD S) in fluids of the Sabga is linke d to bicarbonate salts pr eci- pitated from volcanic ash material at the base of volcanic debris flow. High concentrations in salinity south of this ion rich point source (lahar) are associated with a local maar act- ing as a sink for e lements. This geologic spectacle whereby high salinities have developed in a purely volcanic environment might be linked to the following: ● Explosive volcanic activity leading to the formation of volcanic ash debris flows. ● Massive thickness of the debris and associated struc- tures such as cracks. ● Intense weat hering a nd leachi ng result ing in Ca2+ and enrichment. ● Carbonate/bicarbonate-mineral dissolution by rivers and springs. ● Structural control which further concentrates the Ca2+, and other i ons. Ackno wledgements This article is a part of a M.Sc. thesis on water rock inte- raction at the University of Buea by VRB. We acknowl- edge the support and contributions of colleagues at the University over the years. The editorial comments of the editor are highly appreciated. REFERENCES [1] E. Njonfang, A. Nono, P. Kamgang, V. Ngako and M. F. Tchoua, “Cameroon Line Alkaline Magmatism (C entral Africa): A Reappraisal,” The Geological Society of America Special paper, Vol. 478, 2011, pp. 173-189. http://dx.doi.org/10.1130/2011.2478(09) [2] B. Deruelle, I. Ngounouno and D. Dema if fe , “The ‘Ca- meroon Hot Line’ (CHL): A Unique Examp le of Acti ve Alkaline Intraplate Structure in Both Oceanic and Conti- nental Lithospheres,” Comptes Rendus Geoscience, Vol. 339, No. 9, 2007, pp. 589-600. http://dx.doi.org/10.1016/j.crte.2007.07.007 [3] J. J. Fitton, “The Benue Trough and the Cameroon Lin e — A Migrating Rift Syste m in W es t Africa,” Earth and Planetary Science Letters, Vo l . 51, No. 1, 1980, pp. 132- 138. http://dx.doi.org/10.1016/0012-821X(80)90261-7 [4] D. C. Lee, A. N. Halliday, J. J. Fitton and G. Poli, “Iso- topic Vari ations with Distan ce and Time in the Volcan ic Islands of the Cameroon Line: E vi dence for a Mantle P lume Origin,” Earth Planetary Science Letters, Vol. 123, No. 1-3, 1994, pp. 119-138 http://dx.doi.org/10.1016/0012-821X(80)90261-7 OPEN ACCESS IJG
R. B. VERLA ET AL. [5] J. B. Me ye rs , B. R. Rosendahl, C. G. Harrison and Z. D. Ding, “Deep-Imaging Seismic and Gravi ty Results from the Offshore Cameroon Volcanic Line, and Speculation of African Hotlines,” Tectonophysics, Vol. 284, No. 1-2, 1998, pp. 31-63. http://dx.doi.org/10.1016/S0040-1951(97)00173-X [6] T. Yok oyama , F. Aka, M. Kusakabe and E. Nak a mu r a , “P lu me -Lithosphere Interacti on Beneath Mt. Cameroon Volcano, West Africa: Constraints From 238U-230 Th-226Ra and Sr-Nd-Pb Isotopes Systematics,” Geochimica et Cos- mochi m ica Acta, Vol. 71, No. 7, 2007, pp. 1835-1854. http://dx.doi.org/10.1016/j.gca.2007.01.010 [7] C. E. Suh, R. S. Sparks, J. J. Fitton, S. N. Ayonghe, C. Annen and R. Nana, “The 1999 and 2000 Eruptions of Mount Cameroon: Eruption Behaviour and Petrochemi- stry of Lava,” Bulletin of Volcanology, Vol. 65, No. 4, 2003, pp. 267-283. http://dx.doi.org/10.1007/s00445-002-0257-7 [8] M. Gountie Dedzo, A. Nedelec, T. Nono, T. Njanko, E. Font and P. Kamgang, “Magnetic Fabrics of the Miocen e Ignimbrites from Wes t-Cameroon: Implications for Py- roclastic Flow Source and Sedimentation,” Journal of Volcanology and Geotherma l Research, Vol. 203, No. 3, 2011, pp. 113-132. [9] G. B we l e, “L’encyclopédie de la République unie du Ca- meroun,” Nouvelles Éditions Africaines, Abidjan, 1981. [10] A. S. Neb a, “Modern Geography of the Republic of Ca- meroon,” Neba Publishers, Camd em, 1987. [11] P. Kamgang, E. Njonfang, A. Nono, M. Gountie Dedzo and M. F. Tchoua, “Petrogenesis of a Silicic Magma S ys - te m: Geochemical Evidence from Ba menda Mountains, NW Cameroon, Cameroon Volcanic Line,” Journal of African Earth S ciences, Vol. 58, No. 2 , 2010, pp. 285-304. http://dx.doi.org/10.1016/j.jafrearsci.2010.03.008 [12] P. Kamgang, E. Njonfang, G. Chazot and F. Tchoua, “Géochimie et Géochronologie des Laves Felsiques des Monts Bamend a (Ligne Volcanique du Cameroun),” Comptes Rendus Géoscience, Vol. 339, No. 10, 2007, pp. 659-666. http://dx.doi.org/10.1016/j.crte.2007.07.011 [13] P. Kamgang, G. Chazot, E. Njonfang and F. Tchoua, “Geochemistry and Geochronology of Mafic Rocks from Bamenda Mountains (Cameroon): Source Composition and Crustal Contamination along the Cameroon Volcanic Line,” Comptes Rendus Geoscien ce, Vol. 340, No. 12, 2008, pp. 850-857. http://dx.doi.org/10.1016/j.crte.2008.08.008 [14] I. K. Njilah, H. N. Ajonina, K. V. Kamgang and M. Tchindjang, “K-Ar Ages , Mineralogy, Major and Trace Element Geochemistr y of the Tertiary-Quaternary Lavas from the Ndu Volcanic Ridge N. W. Cameroon,” African Journal of Science and Technology (AJST), Vol. 5, No. 1, 2004, pp. 47 - 56. [15] A. Marzoli, P. R. Renne, E. M. Piccirillo, F. Castorina, G. Bellieni and A. J. Melfi, “Silicic Ma g mas from the Con- tinental Cameroon Volcanic Line (Oku, Bambouto and Ngaoundere): 40Ar/39Ar dates, petrology, Sr-Nd-O Iso- topes and Their Petrogenet ic Significan ce,” Contributions to Mineralogy and Petrology, Vol. 135, No. 2-3, 1999, pp. 133-150. http://dx.doi.org/10.1007/s004100050502 [16] R. Salminen, T. Tarvainen, A. Demetriades, M. Duris, F. Fordyce and V. Gregorauskiene, “FOR EGS Geochemical Mapping Field Manual,” Geological Survey of Finland guide, Rovaniemi, 1998. [17] D. L. Parkhurst and C. A. Appelo, “User’s Guide to PHREE QC (Version 2)—A Computer Program for Spec- iation, Batch-Reaction, On e -Dimen s ional Transport and Inverse Geoche mical Calculations,” US Geological Sur- vey Water-Resources Investigations, Report 99-4259, 1999, p. 310. [18] A. St reckeisen, “To Each Plutonic Rock Its Proper Na me ,” Earth Science Reviews, Vo l . 12, No. 1, 1976, pp. 1-33. http://dx.doi.org/10.1016/0012-8252(76)90052-0 [19] A. Streckeisen, “IUGS Subcommission on the Systematics of Igneous Rocks Classification and Nomenclature of Volcanic Rocks, Lamprophyres, Carbonatites and Meli- litic Rocks. Recommendatio ns and Suggestions,” Neu es Jahrbuch für Mineralogie Stuttgart, Vol. 134, 1978, pp. 1-14. [20] A. Streckei sen, “Classification and Nomenclature of Vol- canic Rocks, Lamprophyres, Carbonatites and Melilitic Rocks: Recommendations an d Suggestions of the IU GS Sub Co mmi ssio n on the Systematics of Igneous Rocks : Geology,” The Geological Society of America, Boulder, Vol. 7, No. 7, 1979, pp. 331-335. [21] R. S chmi d , “Descriptive Nomenclature and Classification of Pyroclastic Deposits and Frgments: Recommendations of the IUGS Subcommission on the Systematics of Igne- ous Rocks: Geology,” The Geological Society of A mer ica, Boulder, Vol. 9, No. 1, 1981, pp. 41-43. [22] M. J. Le Bas and L. R. W. Maitre, A. Streckeisen and B. Zanettin, “A Chemical Classification of Volcanic Roc ks Based on Total Alk al i -Silica Diagram,” Journal of Pe- trology, Vol. 27, No . 3, 1986, pp. 745-750. http://dx.doi.org/10.1093/petrology/27.3.745 [23] Beeson , “Alkali Olivine Basalt , S a mp l e KLPA-1, East Molokai Volcanoe Hawaii,” In: R. A. Loren, Ed., Petrolgy: The Study of Igneous, Sedimentary and Metamorphic Rocks, 2nd Edition, McGraw-Hill, New York, 2002, pp. 102-103. [24] Coats, “Circle Creek Rh yolite, Sampl e 60NC145, Elko Country, Nevad a,” In: R. A. Loren, Ed., Petrology: The Study of Igneous, Sedimentary and Metamorphic Rocks, 2nd Edition, McGr a w-Hill, New York, pp. 126-127. [25] W. Cross, J. P. Iddings, L. V. Pirsson and L. V. Wa sh- ington, (1903): “Quantitative Classification of Igneous Rocks,” University of Chicago Press, Chicago, 1903. [26] C. H. Kelsey, “Calculation of CIPW No r m,” Mineralogi- cal Magazine, Vol. 34, 1965, pp. 276-282. http://dx.doi.org/10.1007/s004100050502 [27] E. P. Thornton and O. E. Tuttle, “Chemistry of Igneous Rocks-Differentiation Index,” American Journal of Sci- ence, Vol. 258, No. 9, 1960, pp. 664-684. http://dx.doi.org/10.2475/ajs.258.9.664 [28] H. A. Gorrell, “Classification of Formation Waters Based on Sodium Chloride Content,” American A sso ciat i on of Petrol eum Geologists Bulletin,” Vol. 42, No. 10, 1958, pp. OPEN ACCESS IJG
R. B. VERLA ET AL. 2513. [29] A. M. Pip er, “A Graphic Procedu re in the Geochemical Interpretation of Water An a lyse s,” Transactions, Ameri- can Geophysical Union, Vol. 25, No. 6, 1944, pp. 914- 923. http://dx.doi.org/10.1029/TR025i006p00914 [30] G. Z. Tanyileke, M. Kusakabe and W. C. Evans, “Che- mical and Isotopic Character istics of Fluids along the Cameroon Volcan ic Line, Cameroon,” Journal of African Earth Science, Vol. 22, No. 4, 1996, pp. 433-44. http://dx.doi.org/10.1016/0899-5362(96)00025-5 [31] C. Dessert, B. Dupre, J. Gaillar det, M. Francois and C. Allegre, “Basalt Weathering Laws and the Impact of Ba- salt Weatherin g,” Chemical Geology, Vol . 202, No. 3-4, 2003, pp. 257- 273. http://dx.doi.org/10.1016/j.chemgeo.2002.10.001 [32] R. J. Gibbs, “Mechanisms Controlling Wor ld Water Che- mistry,” Science, Vol. 17, No. 8, 1990, pp. 1088-1090. [33] S. M. Yidana, B. B anoeng-Yakubo and P. A. Sakyi , “Identifying Key Processes in the Hydrochemistry of a Basin through the Combined Use of Factor and Regres- sion Models,” Journal of Earth System Science, Vol. 121, No. 2, 2012, pp. 491-507. http://dx.doi.org/10.1007/s12040-012-0163-0 [34] A. L. Mar echal, “Géologie et Giochimie des So urces Th ermo-minérales du Cameroun,” Travaux et Documents de L’orstom N0 59, Orstom, Par is, 1976. [35] N. S. Davis and J. R. De Wiest, “Hydrogeology,” Wiley & Sons Inc., New York, 1966. [36] H. Shinohara, W. Giggenbach, M. Kusakab e and T. Ohba, “Formation of Acid V olcanic Brines through Interaction of Magmatic Gases,” Geochimica et Cosmoch i mi ca A cta, Vol. 67, No. 18, 2003, p. 433. [37] E. J. L ynn, “Geographic Information Sys t ems in Water- Resources Engineering,” CRC Press (T ayl or & Francis Group), Boca Raton, 2009. [38] A. Abdul-Rahman and M. Pilouk, “Spatial Data Model- ling for 3D GIS,” Springer, New York, 2008. [39] A. P. Gretchen, “GIS Cartography: A Guide to Effective Map Design,” CRC Press ( Tayl or & Francis Group), Bo- ca Raton, 2009. OPEN ACCESS IJG
|