Exploration for gold bearing alteration zones in South Eastern Sinai, Egypt: using Landsat TM imagery
Talaat M. Ramadan* and Hassan Bekheit**
*National Authority for Remote Sensing and Space Sciences, Cairo, Egypt.
**Geological Survey of Egypt
[email protected] hotmail.com
In the present work, Landsat TM imagery are used to identify the location and extent of the gold bearing alteration zones in the South Eastern part of Sinai. 5/7, 5/1 and 5/4x3/4 Landsat TM rationing images useful for the regional mapping of lithology and structures in the study area. The rationing images (5/7-5/1-4) distinguish different types of alteration zones at Wadi Kid, El Samra and Wadi Shallal areas.
The study area is underlain by Neoproterozoic island arc metavolcano-sedimentary rocks, metavolcanic rocks (host the alteration zones) and gabbro-diorite rocks. They are cut by younger volcanics and intruded by granitic rocks.
Landsat Thematic Mapper (TM) data and field work is combined with mineralogical and geochemical data showed two different types of alteration zones (Zone l and Zone 2). Zone 1 is close to the metvolcano-sedimentary rocks at Wadi kid and Wadi Samra areas, whereby zone 2 is located within the granodiorite rocks and occur at Wadi Shallal area. Both of these alteration zones are concordant with the main NW-SE structural trend and appear to extend northwards of the study area.
Mineralogical studies indicate that the alteration zone 1 consists mainly of muscovite, quartz, albite, garnet and andalusite. Gold, sphalerite, arsenopyrite, chalcopyrite, pyrite, pyrrhotite, ilmenite, bornite and covellite are the main ore minerals within this zone.
The alteration zone 2 contains chlorite, albite, illite, mucovite, quartz, epidote/clinoyzosite, gold, chalcopyrite, molybdenum, hematite, rutile, ilmenite and magnetite.
The geochemical analysis for samples from alteration zones 1, recorded presence of relatively high contents of Au, Ag, Cu, Pb, Zn elements. The gold (Au) content reaches up to 15 g/t, silver (Ag) up to ….. g/t, lead (Pb) up to 28 %, zinc (Zn) up to 0.59 %, arsenic (As) up to 0.2 %, and antimony (Sb) up to 0.24 %. The geochemical analysis for samples from alteration zones 2, recorded presence of relatively high contents of Au, Ag, Cu, Mo and W elements. The gold (Au) content reaches up to 3.5 g/t, silver (Ag) up to ….. g/t, molybdenum (Mo) up to 0.74 % and tungsten (W) up to 0.16 %.
This study demonstrates the utility of orbital remote sensing for finding unknown alteration zones and related ore deposits in southern Sinai and other arid regions.
The studied area lies between latitude 28ْ 10َ 00ً & 28ْ 30َ 00ً N and longitudes 34ْ 15َ 30ً & 34ْ 24َ 40ً E.
Khashim El Fakh locality was previously considered as a target for copper mineralization and many old works are observed along several shear zones distributed in the locality.
These mineralized occurrences are located in include two areas. Umm Zerriq-kid area is located in the northwestern part, while the El Samra area is located in the southeastern part the asphaltic road between Sharm El Shekh and Dahab cities connect between the two areas with distance about 25 Km.
The present study aims at studying geology, petrography and geochemistry of some mineralized occurrences in southeastern Sinai along the Gulf of Aqaba, Wadi El kid.
- Remote sensing analysis:
- Field working
More than 232 samples representing the different dock varieties were collected along different geological profiles and digged trenches ,as well as the drilled borehole The collection of samples had been carried out using global position system (GPS) as a New technique in survey. Sampling in the investigated area had been carried out through a network of profiles ,trenches ,and stream sediments where the bed-rock ,channels and alluvial sample had been collected respectively to represent all rock varieties.
Several detailed geological maps and sketches were prepared at different scales (1:10,000,1:40,000 and 1:2000) for the different locations sites I, II, and III in Umm Zerriq-kid area .
- Laboratory work
More than 121 thin sections and polished surfaces had been prepared for studying the petrography of the rocks and ore minerals. The most of samples had been analyzed in the central laboratories of the geological survey of Egypt. Moreover 43 bed rock samples were analyzed for ore metals in southern Africa.
Several techniques of analysis had been used including Atomic Absorption technique (Model ). The trace elements Au, Ag, Cu, Pb, Mo and Zn were analyzed by using Atomic Absorption spectroscopic method. The inductive coupled plasma (ICP) technique as used to analyze 43 rock samples, collected from Umm Zerriq-kid area, for Au, Ag, Cu, Pb, Zn, Sb, C, Ni, Co, Fe, S and Mn.
III. RESULTS AND DISCUSSION:
3.1: Lithological Interpretation:
- Wadi kid area
Wadi kid area is located between Lat. N and Long. E. It is covered mainly by rocks of meta volcano -sedimentary successions of the kid group. The oldest rock unit in this area is the metasediments (chlorite, biotite, garnet and andalusite schists) intercalated with the metatuffs (crystal and lithic metatuffs). These rocks possibly have been formed in low to medium grade regional metamorphism of green schist and the beginning of amphibolite grade. The metasediments are intruded by some masses of Feirani volcanics (Abu El Leil, 1992) characterized by their porphyritic texture. Sometimes, some masses of silicified carbonate meta-tuffs are mainly observed in the western side of the area. Several basic to acidic dykes differing in thickness and composition cut the area. Umm Zerriq-kid area is highly affected by large sets of structural elements reflecting different tectonic movements which had been happened through the different geological periods. According to the field observations and measurements, at least three phases of deformation are easily recognizable which reflect many types of lineation, folding, faulting, thrusting, gneissosity, cleavages and shear zones. The area is intensely folded and revealed many major and minor folds. The eastern part of the mapped area at sites II and III at Wadi kid are highly folded than the western part at site I Wadi Umm Zerriq. Many recumbent, tight, disharmonic, conjugate, open and ptygmatic folds are recorded with axial planes parallel to the general orientation of the foliation, but sometimes perpendicular to it. The general major folds trend NW-SE. The shear zones are observed in the schists and the metatuffs particularly associated with thrusting which are observed along both Wadi Umm Zerriq and Wadi kid at the three sites and highly revealed in the eastern side of the area at site II. These mineralizations are exposed at the surface and occupy about 7 km2, As well as their subsurface extension reaches up to 100 m (at site II ) as the collected core samples from the drilled bore- hole indicated. Structurally the mineralizations are highly controlled where the highly mineralized zones occur in highly deformed zones. Also the mineralization potentially increases with increase of the grade of metamorphism.
Geologically, the site is composed mainly of extensive altered schists (biotite schist, garnet schist and garnet andalusite schist ) intersected by several trachytic and doleritic dykes trending NNE –SSW. These dykes vary in thickness from 2 m (doleritic dykes) to more than 7 m (trachitic dykes) and extend up to 1km. The succession is folded into a series of anticlines and synclines trending ENE_WSW. It was also subjected to low-pressure metamorphism in several aureoles (Shimron and Zwart 1970, Reymer et al., 1984).
- El Samra area
El Samra area is built up mainly of metavolcano-sedimentary succession (chlorite biotite schist and crystal lithic tuffs), Feirani volcanics (rhyodacites) and dyke system. Molybdenum-copper bearing stockwork is observed cutting across the crystal lithic tuffs. Gold bearing gossan and rhyolitic dykes are hosted in both chlorite biotite schist and rhyodacite porphyry of Feirani volcanics. Many altered sheared belts are found stained by copper mineralization. The chlorite biotite schists are recorded in the mapped area in two locality, at the stockwork and sulphide location. They occur as greenish gray color, fine to medium-grained, strongly foliated elongated belts. The schistosity is striking NE-SW, with angle of dip varying from 300-400 toward east. The crystal lithic tuffs form low hills, occupying the foot of the chlorite biotite schist and considered the host rock of the Mo-Cu-bearing stockwork and Cu bearing sheared rock. The rocks show bedding planes with dip 400 -600 to SSE and striking generally NE. Feirani volcanics appear in variable colors (gray, grayish green, black and pinkish gray), highly jointed sometimes weathered, altered, brecciated and xenolithic. Several basic and acidic dykes are observed cutting all rock units of the investigated area with various trends. The main one striking NE-SW with thickness up to 3 m and extends more than 400m.
- El Shallal area
III. 2. Gold mineralization
The gold mineralization associated with two types of alteration zones at the study area. Alteration zones of type 1 occur in the metavolcano-sedimentary rocks at Wadi Kid and El Samra areas, and type 2 are associated with the granodiorite rocks at Wadi El Shallal area (Fig. ).
- Gold mineralization at Wadi Kid area:
The gold mineralization at Wadi kid area associated with mainly with alteration zones, quartz veins and gossans. Landsat TM images indicate presence of huge alteration zones at three sites along Wadi Umm Zerriq and Wadi Kid (Fig. ).
These alteration zones occur as elongated bodies, extending parallel to the schistosity forming bodies, trending NW-SE and dipping to the north and NNW - SSE with angle ranging from 30°-50°. These alteration zones extend up to 500 m with about 2 - 20 m in thickness. These alteration zones are characterized by silisification, kaolinitization and ferrugenation and hosted in high grade metamorphosed volcano-sedimentary rocks. Most of these mineralizations are exposed at the surface and occupy an area of about 7 Km2, as well as their subsurface extension at site II reaches up to 100 m (Reference, ). Mostly, they are highly disseminated with galena, aresnopyrite, pyrite and copper mineralization (chalcopyrite, bornite, covellite and malachite).
Several types of quartz veins associated with the alteration zones are recorded at Wadi kid area. They include milky, smoky and iron oxides-bearing quartz veins. Most of these quartz veins are deformed and concordant with the schistosity. The main bulk of these quartz veins is recorded in the eastern side of Wadi Um Zerriq and Wadi Kid relative to the western side. Some parallel sheeted quartz veins rich in iron oxides are found along Wadi Umm Zerriq cutting across the metatuffs. They vary in thickness from few centimeters to about 40 cm and extend to more than 40 m. Visible pure galena was observed mixed with deformed smoky quartz lenses at site II located at Wadi Kid.
The gossans are found mainly associated with the alteration zones and hosted in the metavolcano-sedimentary rocks. They are as multicolor rounded and elongated pockets, distributed along the alteration zones, ranging in diameter from 2 x 3 m to 30 x 40 cm. They are widely distributed in the northern part of Wadi Kid and characterized by their limonite colour. They are composed mainly of hematite with subordinate limonite and carbonates. They are found in two forms; as thin layers cap the alteration zone and as large semi-rounded lenses . the thin layers of gossans extend parallel to the alteration zone, varying in thickness from 7 cm to 20 cm and extend up to 200 m. and trending NW-SE. The large lenses of gossans are distributed along the alteration zones. They are composed mainly of greenish limonite iron oxides, partially stained with iron oxides (mainly hematite). Another type of large lenses are recorded in the from a limonite yellow semi-rounded lenses, with diameters ranging from 50 cm x 40 cm to 2m x 3m and are composed mainly of limonite yellow iron -oxides , massive and less altered than the greenish limonite ones. Spongy texture is clearly observed in this type, and the gossans of this site are promising for gold, silver and lead mineralization.
The field observation showed that the highly mineralized zones occur in the highly deformed zones. Also it is obvious that the mineralization potential increases with the increase of the grade of metamorphism. Structurally, these sites are located at the intersection of major faults trending mainly NNW-SSE and NNE-SSW. Several minor folds are recorded in these sites reflecting polyphases of deformation affected the area .
III. 2. Gold mineralization at El Samra area:
Landsat TM and field studies reveal several alteration zones at the study area. These alteration zones are recorded at three sites namely: Khashm El Fakh (Site – 4), Stockwork (Site – 5), Sulphide (Site – 6). They have been subjected to intensive field work to follow up the promising rock units for mineralization aspects. These zones are associated with mineralized quartz veins, gossans, and iron bands hosted in metavolcano-sedimentary rocks (schists and tuffs) and rhyodacitic rocks of Feirani volcanics. Most of mineralization are recorded at the surface and controlled by several intersected faults and some folding system.
The alteration zones appear as a greenish yellow, elongated belt hosted mainly in rhyodacitic rocks and there related tuffs. They are ranging in thickness from 20 cm to 2 m and extending up to 200 m, trending mainly NW-SE and NNE-SSW and nearly vertical. They are present in two localities (Khashm El Fakh locality (Site – 4), and Stockwork locality (Site – 5)) and show tangible mineralization in Au, Cu and Mo.
Several types of quartz veins are recorded at the studied localities, hosted mainly in the crystal lithic tuffs and the chlorite biotite schists. These types include two main types: milky quartz veins stained by iron oxides and small smoky veinltes of quartz rich in iron oxides. The former one is found in the form a network of stockwork, hosted in the crystal lithic tuffs at stockwork locality and show tangible Mo-Cu mineraliztion. The later one is hosted in the chlorite biotite schist at the sulphide area and show abnormal values in gold mineralization.
The gossans are recorded mainly associated with the chlorite biotite schists and the pyrite-bearing rhyolite at the sulphide locality. They occur in two forms, as multicoloured elongated pockets rich in iron-oxides concordant with the schistosity of the chlorite biotite schists and as spongy bands of iron oxides capping the pyrite-bearing rhyolite. They range in thickness from 5 cm to 15 cm and extended more than 150 m. They host abnormal values of Au.
Banded Iron Formation is recorded mainly associated with the alteration zones at Khashm El Fakh locality. They are ranging in thickness from few centimeters to more than 4 m extending up to 50 m in length and trending NW-SE. They are present in three forms; as massive lenses, thin veinlets and bands. The thin iron veinlets are considered the promising ones for Cu-mineralization.
The detailed description for the mineralization in each of above localities will be discussed hereunder :
A- Stockork locality :
Three mineralized rock units were recorded at the stockwork locality including stockwork, altered tuffs and altered sheared zones, hosted mainly in the crystal lithic tuffs ( Fig.129)
The stockwork is found as series of intersected quartz veins and veinlets close to each other forming a network occupying an area 300 x 350 m and cutting across mainly the crystal lithic tuffs and rarely the chlorite biotite schists. These veins vary in width from 7cm to 40 cm, where their length extending few meters, trending many directions;NNE-SSW, E-W and NW-SE, stained by iron oxides (hematite and limonite). These veins are highly affected by many deformational events which appear clearly through a large network of microfractures, stained by some malachite mineralization and folded veins. The stockwork shows tangible abnormal values of Cu and Mo mineralization.
2- Altered metatuffs :
The altered metatuffs of the crystal lithic type occupy an area 350mx400 m and hosting the stockwork. They vary in colour from yellowish grey to greenish grey colour and highly affected by chloritization, epidotization and kaolinitization. These types of altered tuffs related to the stockwork show some tangible abnormal values for Mo and Cu mineralization.
3- Sheared Zone:
The sheared zones in the stockwork locality is characterized by its thin thickness, vary from 10 cm to 30 cm and extending up to 100 m, trending NNE-SSW. They are stained by iron oxides and epidote minerals. This sheared zone shows abnormal values for Cu-mineralization.
2- Sulphide locality :
The mineralization at the sulphide locality is confined to the main rocks hosting gossans, iron oxides-bearing quartz veinlets, pyrite-bearing rhyolite and talceous lenses. They are hosted in the chlorite biotite schist and the rhyodacitic porphyry of the Feirani volcanics.
These gossans are recorded mainly in two forms; the first as small elongated lenses associated with some smoky quartz veinlets, rich in iron oxides, trending NE-SW, concordant with the bedding of the chlorite biotite schists at their contact with the rhyolite porphyry, with width does exceeding 15 cm and extending for about 150 m ( Fig. 135 ). The second form is a thin layer capping some pyrite-bearing rhyolitic dykes, characterized by its dark brownish weathered surface and multicoloured fresh surface, with boxwork texture, vary in thickness from 5 cm to 15 cm, trending mainly NNE-SSW direction. These gossans are promising for gold mineralization.
2- Quartz veins:
There are two types of quartz veins recorded in this area including; iron-oxides- bearing quartz veinlets and milky quartz.
a- Iron oxides bearing quartz veinlets:
Iron oxides bearing quartz veinlets are recorded concordant with the schistosity of the chlorite schist in the investigated locality, associated with lenses of gossan trending NE-SW, and vary in width from 3 cm to 7 cm and extending for about 150 m.These veinlets are multicoloured (orange. brown and yellow) and are found intensively at the contact with the rhyolite porphyry of the Feirani volcanics.This type of the quartz veinlets is promising for gold mineralization.
b-Milky quartz :
The milky quartz veins at this locality are stained by iron oxides, vary in thickness from 15 cm to 30 cm and extending up to short distances, varying from 1m to 4m. They are trending mainly E-W and hosted mainly in the rhyodacite porphyry of the Feirani volcanics. The quartz veins of this type not show any tangible mineralization.
4- Talceous lenses :
The talceous lenses are present as small pockets composed mainly of muscovite minerals associated with some albititic masses and lenses of milky quartz, hosted in the rhyodacitic porphyry of the Feirani volcanics. They are varying in thickness from 5cm to 15cm and extending up to 2m. This type of lenses shows some gold mineralization.
C- Khashim El Fakh locality:
The mineralization in this locality is confined mainly to main two rock units including; the altered sheared zones and iron lenses.
1- Altered sheared zones:
Several sheared zones were recorded in the investigated locality striking mainly NW-SE, ranging in thickness from 1m to 3m and extending up to 200 m. They are hosted mainly in the acidic volcanic rocks (rhyodacite) and their pyroclastics (the crystal lithic tuffs) of the Feirani volcanics. These zones show intensive brecciation, kaolinitization, carbonization, chloritization, sericitization( Fig.138) and stained by copper mineralization (malachite-azurite). Some iron bearing-lenses and veinlets are present extending along the strike of these sheared zones. The shear zones of this locality are promising for gold and copper mineralization( Fig. 139).
2- Iron bearing lenses and veinlets:
These lenses and veinltes of the iron oxides are found associated with the shear zones, trending NW-SE and dip subvertically, recorded in three forms; banded iron formation, massive iron, iron bearing-breccia dyke. The banded iron formation is composed of bands of iron Oxide (hematite and magnetite) alternating with some chert and quartz and observed interbedded within the pryoclastic rocks, with small width not exceeding than 15 cm and extending more than 20 m. The massive iron formation is found as small lenses, associated mainly with the sheared zones and stained by copper mineralization, with width varying from 10 cm to 25 cm and extending up for less than 10 m. Iron bearing-breccia dyke is striking parallel to the strike of the sheared zones (NW-SE) with width reaching up to 50 cm and extending up to 100m.
III. 2. Mineralization at El Shallal area:
III. 3. Geochemistry:
- Wadi Kid Area:
More than 235 representative lateral and vertical samples were analyzed by using several techniques for Au, Ag, Pb, Zn, Cu, Sb, Ni, Co, Cr, Mn, Fe, S, and Ca. These representative samples include 43 doted samples collected along three profiles ( a profile for each site ) and analyzed by using ICP Technique. Channel samples collected along three trenches ( a trench for each site) and were analyzed by using Atomic Absorption spectroscopy method.
According to these results and their frequency distortion (Table 7) several anomalous values of the following metals can be delineated for Au, Pb, Ag, As, Zn, Cu, and Sb.
Gold (Au ) :
The frequency distribution of gold content shown in table shows that the gold anomalous values are recorded in many rock varieties ( gossan, altered rocks and quartz veins ), it ranges from 0.3 ppm to 15 ppm in the channel samples and from 1ppb to 92 ppm in the profile samples. The average content of the channel samples show increase from site I (0.3 ppm ) to site III (2.7 ppm) through Site II (0.5 ppm ). In this respect the profile samples average content increases from site I (9.3 ppb) to site III (14.3 ppm) through site II (11.5 ppb ). The isoconcentration lines (Fig. 94) of gold show abnormal concentration at site III .The gossan at site III is the main rock variety containing the highest gold values (36 ppm ) (Table 9), as well as the white mica bearing smoky quartz (2.5 ppm ) and the garnetiferous altered rocks (2 ppm ) at site II ).
Silver ( Ag ) :
Silver is considered one of the main highly distributed elements with high contents. It is recorded in the most of collected samples from the 3 sites, it ranges in content from 1 ppm to 92 ppm (profile samples ) and from 0.66 ppm to 146 ppm ( channels samples ). The average content of Ag in the profile samples increases from site I (1.5 ppm ) to site site II (21ppm ) then decreases in site III (17.9ppm ) ,while in trench samples it behaves reversibly where it increases from site I (15.2ppm ) through site II (22.1 ppm ) to site III (36.3 ppm ) .The highest values of Ag are recorded in the gossans at site III (146, 130 and 99 ppm ), while the smoky quartz at site II records 82 ppm. Ag shown from the isoconcentration map (Fig. 92), both sites II and III represents the main anomaly for Zn
Lead (Pb ) :
Lead is considered the main anomalous metal in the investigated area at both site II and III as shown from the iso-concentration lines ( Fig 90 ). Its content ranges from 5ppm to 4.66 % in the profile samples and from 60 ppm to 28% in the channel samples. The frequency distribution of lead ( Tables, 7&8 and 9 ) in both types of samples shows that the highest contents are recorded in the trench channel samples rather than the profile samples collected from sites II and III. Alteration zones, gossans and quartz veins represent the main mineralized rock units (>1000-28% ) while the schists and the tuffs contain the lowest content ( 116 ppm). The highest content of lead (28 %) is recorded in the greenish orange gossans at site III, while the garnetiferous altered rocks and brecciated smoky quartz of trench samples from site II bear Pb up to 27% and 10.2% respectively (Table 9). The highest content of Pb, is associated mainly with abnormal values of Zn, As and subordinate Cu values .The ratio of Pb : Zn increase sharply from site I relative to both sites II and III from 5 : 1 to 23 : 1 and 217 : 1 respectively
Zinc ( Zn ):
Zinc is detected mainly associated with Pb but in lesser content, it ranges from 10 ppm to 1905 ppm in the profile samples ( Table 7 ) and from 87 ppm to 5935 ppm in the channel samples ( Table 9). The frequency distribution of Zn. content ( Fig. 97&98 and 99) shows that the green gossan at site III (5784 ppm ) , the alteration zone at site III (5935 ppm ) and the ferruginated gossan (5428 ppm ) at site II represent the main mineralized rock unites exhibiting highly contrast anomalous zinc values. The average content of Zn in trenches decreases southeastward from site I (3256 ppm ) to site III (1187 ) through site II (1901 ppm ), while the average content of Zn in the profile samples from site I, site II to site III are 316 ppm., 492 ppm and 350 ppm respectively As shown from the iso-concentration map ( Fig. 91), both sites II and III represents the main anomaly for Zn.
Arsenic ( As ):
Arsenic is detected in high values, ranging from 3ppm to 7.2% in the profile samples and from 100ppm to 2000 ppm in the trench channel samples. The average content in the profile samples increases from site I (605 ppm ) to site III (9730 ppm ) through site II (1359 ppm .The channel samples show increase in the average content from site I (307 ppm ) to site II (326 ppm ) and site III (427 ppm ) (table 9 ) .As shown in the iso-concentration maps (Fig 93 ) that site III represent the main anomaly for As and the gossan in this site records the highest concentration (7.3 % ) .
Copper ( Cu ) :
Copper is the less abundant metal comparing with Pb, Ag ,As, Zn and Au . It ranges from 19.ppm to 2425 ppm in the channel samples and from 8ppm to 1941 ppm in the profile samples Table (7). The average content of Cu in the channel samples decreases from site I (428 ppm ) and site III (397 ppm ) to site II (274 ppm ) .In the profile samples ( Fig 105) its content decreases from site II (200 ppm ) to site I (182 ppm ) and site II (75 ppm ). The copper highest anomalous values at site III is hosted in gossan (2425 ppm.), while at site II it is hosted in the silicified carbonate metatuffs (1942 PPM ). These anomalous values are easily delineated on the isoconcentation map of Cu ( Fig 95 ).
Antimony is detected in the most collected profile samples, ranging from 5ppm to 2388 ppm, Its average content increases from site I (5.1 ppm ) and site III (108 PPM to site II (260 PPM ). As shown in the isoconcentration map ( Fig. 96), sites II and III represent the main anomaly for Sb. The main anomalous values at site II is hosted in the altered rocks (2388 ppm.), while at site III it is hosted in the gossan (674 ppm) .
- Iron ( Fe ) :
According to the frequency distribution of Fe in the investigated sites iron content ranges from 2083 ppm. to 470348 ppm. Its average content decreases from site I (35647 ppm.) and site III (78333 ppm.) to site II (19455 ppm) as shown from the isoconcentration map of Fe. The high concentration of Fe is mainly recorded at site III (Fig 101) , hosted in gossans and alteration zones.
Lead element is the main element in the profile samples and the associated elements are Zn, Cu and Sb. In the trench samples Ag is the main mineralization element associated with Au, Pb, As, Cu and Ni( Table 10&11)
In the profile samples Ag is the main mineralizalion element while Au, Pb, Sb, Zn and Cu are the associated elements. In the trench samples Pb is the main mineralizalion element and the associated elements are Ag, Au, Zn and Cu ( Table 12&13)
In the profile samples Ag is the main minereliztion element and As, Pb, Sb and Cu are the associated elements.In the trench samples Pb is the main mineraliztion element and Au, Ag, Cu, As and Zn are the associated elements ( Table 14&15)
However Cu shows abnormal CC values in the tuffs at site I and in the schist at sites II &III, while As show extraordinary anomalous CC values in both tuffs and schist.
These results can be summarized in the following geochemical spectra:
- Site I Profiles : Pb, Zn ,Cu ,Sb & Trenches: Ag Au , As , Cu Ni
- Site II Profiles : Ag Au , Pb ,Sb , Zn ,Cu & Trenches: Pb, Ag , An , Zn , Cu
- Site III Profiles: Ag As, Pb ,Cu & Trenches: Pb Au, Ag , Cu , As Zn
- X-RAY DIFFRACTION ANALYSIS
X-Ray Diffraction analysis had been used to detect the mineral assemblages associated ( Table. 18 ) with the highly mineralized rock units at the three sites of Umm Zerriq-Kid area. Therefore, eleven mineralized rock samples showing high anomalous values in Au, Ag ,Pb ,As and Zn were selected and subjected to X-Ray Diffraction analysis. These samples representing smoky quartz, altered sheared rocks and gossans. The Au content is ranging from 0.5 to 9.23 ppm , the Ag content is ranging from 2.65 to 650 ppm, while the Pb content reached up to 27% ( Table 19 ). The As content reaches up to 5000 ppm . Lead, Zn, Au. Cu and Ag elements had been analyzed by using Atomic Absorption (A. A.) method, while As and Ba by using Spectrograph technique.
They also reveal the following:
Site I: Lead element is the main element in the profile samples and the associated elements are Zn, Cu and Sb. In the trench samples Ag is the main mineralizalion associated with Au, Pb, As, Cu and Ni
Site II: In the profile samples Ag is the main mineralizalion element while Au, Pb, Sb, Zn and Cu are the associated elements. In the trench samples Pb is the main mineralization element and the associated elements are Ag, Au, Zn and Cu
Site III: In the profile samples Ag is the main mineralization and As, Pb , Sb and Cu are the associated elements. In the trench samples Pb is the main mineralization elements and Au, Ag, Cu, As and Zn are the associated elements. However Cu shows abnormal C.C values in the tuffs at site I and in the schist at sites II & III, Arsenic shows extraordinary anomalous C.C values in both tuffs and schist.
These results can be summarized in the following geochemical spectra
Site I profile: Pb, Zn, Cu, Sb
Trench: Ag, Au, As, Cu, Ni
Site II profile: Ag, Au, Pb, Sb, Zn, Cu
Trench: Pb, Ag, Au, Zn, cu
Site III profile: Ag, As, Pb, Cu
Trench: Pb, Au, Ag, Cu, As, Zn
At site I the result of trench samples shows strong significance correlation at p.0.99 between the following pairs of elements: Cu-As, Cu-Ag and As-Pb. Weak significant correlation at p.0.95 occurs between the Paris: Cu-Pb, Cu-Zn and Zn-Pb. The results of profile samples of the same site show strong significant correlation at p.0.99 between the following pairs of elements : As -Sb, As -Pb, Sb -Pb, Zn -Pb and Co-Ni, while weak significant at p.0.95 correlation between Cu -Au and Au – Sb. At site II the correlation coefficient of the profile samples show strong significant at p.0.99 correlation between the following pairs of elements : Sb -Cu, Sb -As, Sb -Au ,Sb-Ni, Cu-As, Cu-Au, As -Au and Pb-Ag and show weak correlation between the following pairs of elements : As -Ni , Ni –Au, Pb –Co, Co- Ag and Zn- Cr. Channel samples show only strong significant correlation at p. 0.99 between copper and lead, while the (r) values of the trench samples show strong correlation between the following pairs of elements : Ag -As, Ag-Pb, Ag-Cu, Zn-Cu and Pb -Cu. At site III the (r) values of trench samples show strong significant at p.0.99 correlation between the following pairs of elements Cu-Pb, Cu-Zn, Cu -Au, Pb-Zn, Pb-As, Pb-Ag, Pb-Au, Zn -Ag ,Zn -Au, Ag-Au, Au-As and Zn-As. Weak significant at p.0.95 correlation appears between Cu-As. The profile samples show strong significant at p.0.99 correlation between the following Paris of elements: As-Zn, As-Cu, As-Sb, Zn-Cu, Zn-Sb, Cu-Ag, Cu-Sb, Ni-CO, Ni-Cr and Co -Cr. Weak significant correlation at p.095 appears between As -Au, Pb -Ag and Ag-Sb.
- Geochemistry of El Samra:
At El Samra area, more than fourty six representative lateral and vertical samples from El Samra area were analyzed for Au, Ag, Pb, Zn, Cu, Mo, using Atomic Absorption technique. These representative samples include 16 channel samples collected along three trenches digged at Kashm El Fakh locality and 30 doted samples collected along two profiles at both stockwork and sulphide localities ( a profile for each locality) were analyzed. According to this result and their frequency distribution, several anomalous values of the following metals can be delineated for Cu, Mo, Au and Ag .
The correct pattern of the distribution of the trace elements in various geologic formations were studied through several geochemical parameters to show the main characteristics of the mineralized rocks and their host rocks and to recognize the geochemical background of the elements and reveal any anomalous values to predict the probability of certain contents in the given geochemical population
Geochemical distribution :
According to these results and their frequency distribution several anomalous values of the following metals can be delineated for Au, Ag Cu and Mo. The geochemical results of the investigated localities can be discussed here under :
1- Stockwork locality :
Thirteen samples represent one profile cutting across the mineralized rocks of the stockwork locality were analyzed for Au, Ag, Mo and Cu. From the Table (28), it is clear that the stockwork, tuffs and sheared zone are copper-bearing associated high values of Mo. The statistical treatment would be used to show the abundance and, the characteristics of Cu, Mo and the associated elements in each rocks.
Gold and silver are not detected in most of the collected samples, but few samples show Au content less than 0.3 ppm and Ag content ranging from 0.4 ppm to 1.6 ppm.
Copper is considered one of the main highly distributed element in this locality with high contents. It ranges in content from 50 ppm to 5000 ppm (stockwork) and from 30 ppm to 4000 ppm (altered tuffs). The average content of Cu increases from the stockwork (850 ppm) to the altered metatuffs (1866 ppm), while, the shear zone and the basic dyke recordimg 1600 ppm and 2000 ppm respectively (Table 28 ).
Molybdenum is detected mainly associated with Cu. It ranges from 130 ppm to 5400 ppm (stockwork) and from 27 ppm to 899 ppm (altered metatuffs). The average content of Mo in contrast to Cu increases from the altered metatuffs (356 ppm) to the sotckwork (1185 ppm), however both the shear zone and the basic dyke are recording the lesser content (15 ppm for each one).
2-Sulphide locality :
At Sulphide locality, the abundance of the trace element show that the gold represents the main element. It ranges from 2.4 ppm to 4.8 ppm in gossan and from 0.4 ppm to 2.1 ppm in pyrite-bearing rhyodacite. The highest value of gold is recorded in iron oxides-bearing quartz veinlets (5.8ppm). The average content of gold in talcaceous lenses is 0.34 ppm.
Silver is detected in all the collected samples. It ranges in content from 0.2ppm (talcecous lens) to 3.1 ppm (gossan). The average content of Cu decreases from pyrite-bearing rhyodacite (153 ppm) and quartz veins (134 ppm) to gossan (107 ppm) and the talcecous lenses (35.8 ppm). Molybdenum element ranges in content from 1.1 ppm (quartz vein) to 65.8 ppm (gossan), while, their average of content in pyrite-bearing rhyolite is 7 ppm.
The plots of the averages of the elements content forming the mineralization at the sulphide locality reveal variation in the distribution of the elements relative to each other. Gold and Mo average contents increase from the talcaceous lenses to the gossan passing through the quartz veins, while, the copper average content gradually decreases from the talcaceous lenses passing through the quartz veins and the gossans. Silver average content gradually decreases from the gossans to the quartz veins through the talceous lenses( Fig.147)
3-Kashm El Fakh locality :
At Kashm El Fakh locality, the abundance of the trace elements through the sheared zones indicate clearly that both Au and Cu are the main elements in this locality with associated high values Mo.
Gold content is ranges from 0.33 ppm to 1.33 ppm with average content 0.66 ppm, while, Ag content ranges from 1.48 ppm to 2.72 ppm with average content 2.20 ppm. Copper content ranges from 280 ppm to 2.01% with average content 4066 ppm. Mo content ranges from 7.8 ppm to 34.8 ppm with average content 15.7 ppm ( Table-30).
The plots of the element content of the Khashm El Fakh locality (Fig. 148) reveal variation in distribution of the elements relative to each other. The plots indicate that both Cu and Au show variable distribution while, Mo and Ag show relatively constant distribution along the sheared zone.