The geochemical studies were conducted in an area covering about 15 km 2 of the south side of the Wadi Rumman area, SW Jordan. The study area included a part of a basement of complex exposed rocks in southwestern Jordan. The complexes comprised igneous and metamorphic suites, mostly from the late Proterozoic age. A systematic geochemical sampling was conducted using rock and heavy mineral-panned concentrate of geochemical samples. Fifty rock samples were collected from the granitic rocks, simple pegmatite dyke, quartz veins and alteration zone, which covered the area. Next, 45 heavy mineral-panned concentrate samples were collected from the alluvium in the stream sediment within the catchment area, and the dray was sieved to less than 1 mm grain size. The geochemical samples were analyzed for their trace elements and gold by using Ione Conductive Coupled Plasma Emission Spectroscopy (ICP-AES) and the Atomic Absorption Spectrometer (AAS) at Natural Resources Authority (NRA) Labs. The results of the geochemical analysis indicated the presence of gold and heavy minerals in the study area, a result considered abnormal in the rock samples. A strong positive correlation was recorded of Au with As, Cu and W (r = 0.82, 0.7 and 1.0), as with Mo (r = 0.83), Cu with Pb (r = 0.83), Sn with Mo (r = 0.73), Mo with W (r = 0.97), Zn with W (r = 0.71), and Li with Bi (r = 0.7). These correlations revealed gold associated within the hydrothermal alteration, quartz veins and pegmatite dyke. Abnormal metals such as As and Bi were good path-finders to find Au. The HM samples showed low positive linear correlations among the concentrations of Au with As, Zn and Li, and negative linear correlations of Au with Pb, Sn, Bi and W. The combination of both rock and heavy mineral concentrate samples shows four geochemical anomalous areas of gold and heavy minerals. The geochemical signatures of Au and As in the Wadi Rumman appear to be in the hydrothermal alteration, quartz veins and pegmatite dyke, respectively. Heavy mineral concentration sampling delineated the Au geochemical anomaly in area 1 specificities with the rock geochemical anomaly of area 1.
Geochemical prospecting for minerals includes any method of mineral exploration based on the systematic measurement of one or more chemical properties of the naturally occurring materials. The chemical property measured is most commonly the trace content of some element or group of elements. The reason for recording these measurements is to discover abnormal chemical patterns or geochemical anomalies, related to mineralization. Among the several geochemical prospecting methods used to discover the study area, the heavy minerals and rock geochemical exploration methods were selected and used in the study area, as they were the more effective methods suitable for this type of region. Heavy mineral geochemical samples of less than 1 mm grain size were collected from the alluvium in the stream sediment, which were a useful method of verifying any decision made during the geochemical exploration for minerals, including the transport distance of the gold nuggets and ultimately regarding the origin of the element dispersion halo [
The basement rocks exposed in southwestern Jordan are subdivided into two broad lithostratigraphic complexes, the Aqaba and Araba [
The Qara granite unit contains medium- to coarse-grained, pink- to whitish-pink to light grayish-pink syenogranite to monzogranite. The mesocratic rocks include small mafic clots at the outcrop, highly weathered and cut by dense dykes of rhyolite and quartz veins. The main mineral composition includes quartz, alkali feldspar and biotite with traces of hornblende and phaneritic in texture, particularly along the margins of the zone in contact with the Ishaar unit. Ishaar granite is medium to coarse grained, phaneritic in texture, grey to greenish- grey, which varies according to the granodiorite. Mesocratic, small circular mafic clots with biotite and hornblende are common, cut by dykes of variable compositions of rhyolite, pegmatite and quartz vines. Quartz, alkali feldspar and biotite constitute the main mineral composition. Rashidiyya Aplite Granite is distinguished by fine grain size, micro granite, pink to whitish-pink colors, leucocratic and sugary with aplitic texture. Acidic dykes and thin quartz veins cut through this unit. Quartz alkali feldspar and biotite form the main mineral composition. Salib Arkosic Sandstone Formation, Early Cambrian in age, consists predominantly of yellow, pink, and purple-brown colors, with very coarse- to medium-grained, cross-bedded arkosic and subarkosic sandstone; pebbles to cobble conglomerates are also locally present. Rounded to sub-rounded pebbles of milky-white quartz and pink feldspar are also seen. Umm Ishrin Sandstone Formation includes the middle to late Cambrian age, with brown, red-brown to yellowish-pink and grey colors, of medium to coarse-grained quartz arenite, with rounded granules and quartz pebbles. There are thin beds of fine-grained sandstone and siltstone exhibiting lineation. Secondary ferruginous and manganese ferrous show color banding and oxides with a massive-weathering face and the typical large trough cross-bedding with pebbles, occasionally overturned for sets is common. Angular clastic siltstone in locally eroded channels is evident, close to the gradational upper boundary of the formation;
The geologic structures of the area under study are affected by the tectonic activity that occurred during the late Proterozoic to the early Cambrian for the extension of the Arabian-Nubian shield which plunges to south Jordan [
Two geochemical methods of investigating rocks and heavy minerals were used in the geochemical exploration of the area under study. Sample points were selected from a published 1:50,000 scale topographic and geological map.
Fifty rock chip samples were collected from the outcropping of the granitic rocks, simple pegmatite, dyke, quartz veins and alteration zone, at a density of five samples per 1 km2 (
Forty-five heavy mineral concentrated samples were collected from the alluvium in the stream sediment within the catchment area of the study, at a density of four samples per 1 Km2 (
The trace elements were analyzed by decomposition using Ione Inductively Conductive Coupled Plasma Emission Spectroscopy (ICP-AES) at Natural Resources Authority Labs. A total of 1 g of the powdered (<80 mesh) sample mixed with 3 g of sodium peroxide (Na2O2) were placed in a zirconium crucible, and fused by heating it to 450˚C for 45 mints, to obtain a sinter. Subsequently, 72 ml of deionized water was added to it and stirred for a few mints; then 28 ml of diluted HCl in a ratio 1:1 was added to obtain clear solutions that were used to determine the trace element concentrations.
The Atomic Absorption Spectrometer (AAS), PerkinElmer 3030 Model was used for gold analysis in the Natural Resources Authority Labs. The analytical method consisted of dissolving the Au in the sample by heating with aqua regia solution (3 ml conc. HCl + 1 ml conc. HNO3) plus iron. The gold (Au) was then extracted with methyl isobutyl ketone (MIBK) solution by introducing the organic phase into a pyrocoated graphite furnace and then analyzed for gold using the Atomic Absorption Spectrometer [
The mineral composition identified by using the petrographic microscope and X-ray Diffraction (XRD) by employing a Philips diffractometer with Cu Ka radiation, at the University of Al al-Bayt.
The rock samples study showed leucocratic, holocrystalline and hypidiomorphic to allotriomorphic fine- to medium-sized grains, phaneritic to megaprophyritic in texture. Using the polarizer microscope and XRD, quartz, feldspar, biotite, hornblende and opaque minerals such as iron oxide and magnetite, were the main minerals identified. The secondary minerals included calcite, sericite, kaolinite and chlorite while the rare minerals found were wolframite (W), davite (B) and cassiterite (Sn). The common textures of the rock samples in the study were perthitic, poikilitic interstitial, zoning and polysynthetic twinning. The lithology and petrography of the area under study showed an alteration zone with high concentration of secondary and oxide minerals. These were indications of the mineralization ore minerals which were documented by chemical analysis for gold and the pathfinders for the geochemical association of the elements. The lithology and petrography are summarized in
The earlier regional geochemical survey of the rocks of the Upper Proterozoic (Aqaba and Araba complexes) in southwest Jordan had been conducted for the regional geochemical survey project [
The trace background values of the study area were taken as the mean and median values [
The Pearson’s correlation coefficients from among the concentrations of Au, As, Cu, Pb, Sn, Mo, Bi, W, Zn and Li found in the study of the rock samples are presented in
Sample number | Lithology | Petrography |
---|---|---|
1, 2, 20 | Aplite granite with highly crashed rocks affected by alteration | Granite rock fragments composed of quartz, feldspar, and biotite. Highly fractured crystals of feldspar, quartz, hornblende and epidote. Hornblende occurs in clots giving the rock a mottled appearance. The cemented material consists of calcite and very fine grains of quartz or cryptocrystalline. Quartz was partially metamorphosed to quartzite. |
3, 26 | Alteration granite, fine to medium grain size, mineral composition quartz, feldspar and biotite, with calcite veins associated in the alteration zone | Calcite minerals contain cavities filled with fibrous quartz and opaque minerals. Calcite shows polysynthetic twinning and two cleavage sets (rhomb cleavage). Silica occurs as cryptocrystalline fibrous chalcedony and fine-grains filled the fractures and spaces or voids. Micrographic textures are visible. Iron oxides occur surrounding the voids or separated along the fractures. |
4, 6, 7, 8, 9, 10, 11, 34, 60 | The alteration zone includes quartz veins with highly crashed rocks | The major textures evident are equigranular, interstitial perthitic and poikilitic. Quartz occurs as anhedral and highly fractured crystals, filling up the spaces between the plagioclase crystals. Feldspar occurs as plagioclase, a major component and a few percent of perthite with perthitic texture. More than 40% is plagioclase found as euhedral and subhedral prisms showing zoning and polysynthetic twinning. It is highly weathered and altered to calcite and sericite. Biotite is rare and highly weathered having been altered to iron oxides. |
12, 13, 14, 15, 16, 17, 18, 19, 23, 29, 30, 31, 33 | Thin Quartz veins (2 - 5 cm in thickness), showing a high degree of alteration and crashed rocks, and trace minerals, like Cu and Pb | The major texture is equigranular and spherulitic. It consists of euhedral elongated crystals of quartz and orthoclase as the major minerals due to the intergrowth between quartz and feldspar like a sheaf form. The slide shows cryptocrystalline silica as a banded rock from the veins, thin veins of cryptocrystalline and spherulitic chalcedony associated with sericite and calcite, fine-grained quartz and finally cryptocrystalline and fibrous chalcedony associated with sericite. A few crystals of orthoclase partially altered and sericite. Iron oxides occur as accessories as very fine aggregates. |
21 | Applite granite with green color and alteration | The slide shows felsitic rock composed of feldspar and quartz crystals. The feldspars are altered to sericite and kaolin minerals. Biotite occurs as rare mineral and is altered to chlorite. |
22, 59 | Quartz veins with the secondary green color of the minerals | Graphic texture is observed. The biotite xenocrysts are partially altered to chlorite and iron oxides. Iron oxides and black spots occur as accessories and separated randomly in the groundmass. |
24, 32, 27, 28 | Basaltic dyke cutting the granite host rocks, with quartz veins | This slide shows two types of rock composition, the first being andesite rock. It consists of feldspar and glass. The feldspar (plagioclase) occurs as small laths and shows twinning and zoning. It is predominantly trachytic in texture. It contains black materials which could be volcanic glass or opaque minerals. The second type comprises chalcedony veins cutting the andesite rock. Spherulitic texture is predominant in the dyke and consists of a dense mass of very intergrown quartz and alkali feldspar (orthoclase) needles, radiating from a common nucleus. These spherulites are followed by fine-grained quartz presenting a drusy structure followed by calcite mineral in the middle (forming bands). This dyke is rich in opaque and fine accumulated band-like aggregates separated from the beginning of the dyke to its end. |
35 | Granodiorite, composite of mafic minerals feldspar, Biotite and hornblende | Granular, consertal and poikilitic textures predominate. Anhedral and highly fractured quartz crystals comprise about 30%. Feldspar includes both the orthoclase and plagioclase forms. Plagioclase constitutes more than 45% and occurs as euhedral to subhedral prisms showing zoning and polysynthetic twinning. It has been highly weathered and altered to clay and sericite. Biotite occurs in about 10% of highly weathered rock, altered to chlorite-like masses. |
36 | Granodiorite is a composite of mafic minerals feldspar, and Biotite, with a high degree of alteration | Granular texture; metamorphic rock fragments of the Biotite Schist consisting of quartz, feldspar and biotite. Biotite was partially altered to chlorite and iron oxides; opaque minerals were seen associated with biotite. Crystals (phenocrysts) partially altered to sericite or clay especially at the centre. Feldspar crystals of fractured quartz are visible. All these rock fragments and xenoliths are cemented by fine-grained of quartz. |
---|---|---|
37, 5 | Rhyolite dyke-fine to medium-sized grains of quartz and feldspar | Equigranular and perthite texture is present. Quartz, perthite and orthoclase are the major minerals. Feldspars are altered to clay and biotite to sericite. Rare occurrences of altered muscovite. Opaque minerals as accessories occur as very fine aggregates. |
38 | Granite-fine to medium grains with highly crashed and withering composites of quartz and feldspar | Phenocrysts of zoned plagioclase are altered to kaolin. Cryptocrystalline silica dust is present as cemented material or as veins. Opaque minerals occur as accumulated aggregates. |
39 | Granite-fine to medium grains | The major textures are granular, consertal and poikilitic, consisting of quartz with anhedral crystals and the highly fractured forms constitute about 20%. In some places they occur as clots (fine?grained) between the coarse crystals. Biotite is altered to iron oxides. |
40, 41 | Simple Pegmatite dyke | The major textures include granular, consertal and poikilitic. It consists of quartz: it occurs as anhedral crystals and highly fractured crystals forming about 40%. Feldspar occurs as perthite and shows perthitic texture, is altered to clay forming more than 30%, while the plagioclase forms about 25%. It occurs as euhedral to subhedral prisms showing zoning and polysynthetic twinning. It is highly weathered and altered to clay and sericite. Biotite forms less than 3% and is highly weathered and altered to iron oxides. Iron oxides occur as veins due to a solution rich in Fe. |
42,43, 44, 45,46, 47, 48 | Granite, fine grain size, composed of feldspar and quartz and secondary oxide minerals | Micrographic texture is evident. It consists of fine-grained quartz and orthoclase as the major minerals associated with each other. Plagioclase occurs as a minor mineral. Orthoclase and plagioclase are altered to kaolin and sericite. Biotite occurs in a low percentage, partially altered to chlorite. Iron oxides and calcite occur as secondary minerals filling the fractures and veins. The fractures show a dendritic texture. Phenocrysts of fractured quartz are present. |
49 | Granite, coarse grain size, feldspar, quartz and Biotite constitute the main mineral compositions | The major textures are intergranular, consertal and poikilitic. It consists of about 30% quartz with highly fractured anhedral crystals. Feldspar occurs as both perthite and plagioclase. Plagioclase occurs as euhedral to subhedral prisms showing polysynthetic twinning It has been highly weathered and altered to calcite, clay (kaolin) with sericite as the rim. Perthite occurs as coarse-grained and is perthitic in texture with Carlsbad twinning. Mica sheets (biotite and muscovite) form about 5% and are highly weathered and altered to chlorite and iron oxide like masses. Calcite and iron oxides occur as secondary minerals filling fractures and veins. Opaque minerals occur as accumulated aggregates or masses while zircon occurs as an inclusion in the mica sheet. |
The geochemical anomaly map for the rock samples of Au, As, Cu, Pb, Sn, Mo, Bi, W, Zn and Li are shown in
The heavy mineral (HM) method has been found to be more sensitive for detection and discovery in mineral exploration. This method has been in use for the last 100 years for exploration of gold by panning. The recent, heavy mineral surveys used the concentrates from the drainage sediment samples as beneficial geochemical and mineralogical guides to mineralization [
Au (mg/ton) | As (ppm) | Cu (ppm) | Pb (ppm) | Sn (ppm) | Mo (ppm) | Bi (ppm) | W (ppm) | Zn (ppm) | Li (ppm) | |
---|---|---|---|---|---|---|---|---|---|---|
Number of values | 19 | 35 | 27 | 35 | 46 | 13 | 24 | 11 | 49 | 48 |
Minimum | 5 | 1 | 1 | 1 | 3 | 2 | 1 | 3 | 1 | 5 |
Maximum | 50 | 32 | 120 | 82 | 150 | 50 | 10 | 36 | 200 | 198 |
Mean | 15.4 | 11.7 | 22.63 | 31.2 | 22.85 | 15.8 | 4.1 | 12.7 | 56.8 | 67.4 |
Median | 10 | 10 | 5 | 25 | 17 | 9 | 3 | 9 | 42 | 42.5 |
Average | 15.37 | 11.74 | 22.63 | 31.23 | 22.85 | 15.76 | 4.1 | 12.73 | 56.8 | 67.4 |
Standard deviation | 14.3 | 7.64 | 37.2 | 25.3 | 25.83 | 16.5 | 2.4 | 10.7 | 48.14 | 58.67 |
Threshold 1 = mean + 2 SD | 44 | 26.98 | 97.03 | 73.23 | 82.86 | 48.8 | 8.9 | 34.1 | 153.08 | 184.74 |
Threshold 2 = median + 2 SD | 38.6 | 25.28 | 79.4 | 75.6 | 68.66 | 42 | 7.8 | 30.4 | 138.28 | 159.84 |
Au | As | Cu | Pb | Sn | Mo | Zn | Li | Bi | |
---|---|---|---|---|---|---|---|---|---|
Au | 1 | ||||||||
As | 0.827 | 1 | |||||||
Cu | 0.694 | −0.128 | 1 | ||||||
Pb | −0.019 | −0.032 | 0.833 | 1 | |||||
Sn | −0.178 | 0.156 | 0.093 | −0.088 | 1 | ||||
Mo | −0.264 | 0.829 | −0.015 | −0.079 | 0.726 | 1 | |||
Zn | 0.057 | −0.040 | 0.0285 | 0.340 | 0.269 | 0.007 | 1 | ||
Li | −0.004 | −0.071 | 0.376 | 0.180 | 0.194 | −0.007 | 0.4 | 1 | |
Bi | −0.200 | 0.276 | −0.148 | −0.331 | 0.165 | 0.529 | 0.085 | 0.657 | 1 |
W | 1.000 | 0.675 | −0.413 | 0.696 | 0.032 | 0.967 | 0.706 | −0.041 | −0.030 |
studies provided high-energy sediments in dry arid climates.
The geochemical data analysis for HM was treated to get the results of the geochemical statistics and maps of the geochemical anomalies
The geochemical anomaly map for the HM samples of Au, As, Pb, Sn, Bi, W, Zn and Li is shown in
Au (mg/ton) | As (ppm | Pb (ppm) | Sn (ppm) | Bi (ppm) | W (ppm) | Zn (ppm) | Li (ppm) | |
---|---|---|---|---|---|---|---|---|
Number of values | 14 | 46 | 44 | 37 | 5 | 17 | 39 | 45 |
Minimum | 5 | 1 | 15 | 3 | 4 | 9 | 38 | 10 |
Maximum | 30 | 37 | 123 | 140 | 38 | 82 | 292 | 49 |
Mean | 10.6 | 13.00 | 64.34 | 48.24 | 21.80 | 34.70 | 193.60 | 26.00 |
Median | 10 | 11.00 | 65.00 | 51.00 | 24.00 | 31.00 | 190.00 | 24.00 |
Average | 10.64 | 12.97 | 64.34 | 48.24 | 21.80 | 54.71 | 193.61 | 26.04 |
Standard deviation | 5.96 | 8.62 | 28.75 | 36.20 | 12.90 | 21.00 | 69.94 | 10.60 |
Threshold 1 = mean + 2SD | 22.52 | 30.20 | 121.84 | 120.64 | 47.60 | 76.70 | 333.48 | 47.20 |
Threshold 2 = median + 2SD | 21.91 | 28.24 | 122.50 | 123.40 | 49.80 | 73.00 | 330.48 | 45.20 |
HM | Au | As | Pb | Sn | Bi | W | Zn |
---|---|---|---|---|---|---|---|
Au | 1 | ||||||
As | 0.39 | 1 | |||||
Pb | −0.01 | 0.08 | 1 | ||||
Sn | −0.19 | 0.49 | 0.27 | 1 | |||
Bi | −0.30 | 0.44 | 0.22 | 0.16 | 1 | ||
W | −0.30 | 0.48 | 0.26 | 0.09 | 0.60 | 1 | |
Zn | 0.01 | 0.20 | 0.58 | 0.29 | −0.04 | 0.46 | 1 |
Li | 0.02 | 0.20 | 0.56 | 0.02 | −0.05 | 0.51 | 0.17 |
vealed the association of the metals in alteration with the host rocks and accumulated within the sediment deposits. According to [
Detailed geochemical investigations of the rock and stream sediments for the HM samples were done during the geochemical exploration for the study area. High background values of metals at a hydrothermal alteration zone have been discovered, naturally. The discovery of the south Wadi Rumman area prospect during the following up of an already delineated anomaly has been a successful exploration using rock and <1 mm heavy mineral sediment geochemistry. Moreover, the sampling technique was proven to be a very sensitive exploration tool even in the discovery of small-scale mineralization, in areas having well-developed drainage, as in the Wadi Rumman area. Identification and sampling of the altered and mineralized rocks, which floated in the streams, were critical in categorizing the details of the geochemical results [
The author is thankful to the Natural Resources Authority for assistance in geochemical analysis and to ICP- AES and (AAS) for their contribution to the project “Detailed Geochemical Prospecting Minerals for Proterozoic granitoids, Southwest Jordan”. The author is indebted and grateful to the anonymous reviewers for their comments and assistance in improving the manuscript quality.
I.A.A.Bany Yaseen, (2015) Geochemical Exploration for Gold and the Association of As-Cu-Pb-Sn-Zn-Li in the Upper Proterozoic Granitoids of the Wadi Rumman Area, Southwest Jordan. International Journal of Geosciences,06,1140-1153. doi: 10.4236/ijg.2015.610089