MINERAL POTENTIAL OF THE EASTERN PART OF WADI ALLAQI, SOUTH EASTERN DESERT, EGYPT

Annals Geol. Surv. Egypt , VXXIV (2001 ) , PP ,

Ahmed, A.M., Said, M.M., El Baghdady, M.M and Abdel Wahab, G.

Egyptian Geological Survey

ABSTRACT

An area of 3750km2 at the eastern part of Wadi Allaqi was geochemically prospected for mineral deposits. The rock units encountered are monzogranite and alkali feldspar granite , younger gabbro, tonalite – granodiorite schistose mtavolcanics and related pyroclactics metagabbro, serpentinite and related rocks ,and psammitic- pelitic rocks “metasediments”. Alteration zones were recorded usually associated with quartz veins and veinlets.

A total of 1218 stream sediment samples, 151 bed rock samples “from alteration zones and quartz veins and 25 samples for panning were collected. The stream sediments were subjected to semiquantitative spectral analysis. Fifty one bed rock samples and 19 panning samples were analyzed by atomic absorption techinque for Au, Cu, Cr, Ni and Co.

The results of spectral analysis for stream sediment samples were statistically treated for Cu, Cr, Ni, V, Zr, Ba and Sr. Copper values varied from 3 ppm to 300ppm ,average 27 ppm. Chromium concentrations ranged from 100 to 10000ppm with an average of173ppm. Nickel values ranged from 10 to 1000ppm , average 48ppm. Vanadium contents ranged from 10 to 200 ppm , average 62ppm. Barium values ranged from 100 to 2000ppm , average 373 ppm. Strontium values ranged from 100 to 1000ppm with an average of 247ppm.

Gold contents in the alteration zones ranged from 0.3 to 11g/t . The average is 0.4 g/t. The high contents (2-11) g/t were in three samples around Betam area and (1.8-4.2) g/t in two samples around Um El Tuyur El Fugani area.

The concenterates of the panned samples gave gold contents ranging from 3.75 to 36.7 g/t in 4 samples from El Hatieb area, and from 2- to 6 g/t in two samples from Betam area.

INTRODUCTION

The eastern part of Wadi Allaqi, south Eastern Desert is bounded by Lat 22o 00` 00`` - 22o 30` 00`` N. and Long . 34o 00` 00`` - 34o 45` 00``E.

The area covers about 3750 km2, and was not systematically explored before So;during the season 1995-1996 a regional geological and geochemical prospecting program was carried out on scale 1:100,000 in fulfillment of the Geological Survey program aiming at the location of the occurrences of economic mineral deposits.

The rock units of the area were mapped by Sadek et al. ( 1995 )as psasmmitic – pelitic rocks, serpentinite, metagabbro, schistose basic to intermediate metavolcanics and related pyroclastics, schistose intermediate to acidic metavolcanics and related pyroclastics, foliated tonalite-granodiorite, quartz gabbro, intrusive ultramafic, fresh gabbro, tonalite-granodiorite, monzogranite and alkali feldspar granite.

This paper presents the results of that survey outlining the geochemical anomalies some of which would need further investigation.

GEOLOGICAL SETTING

On the basis of field observations, the following rock units are recognized, from oldest to youngest “Fig 1”.

1. Metasediments “Psammo - pelitic Rocks” :-

These rocks form low relief and are fine to medium-grained. Regional deformation is pronouced causing foliation of a general NE-SW trend. The rocks are strongly deformed and folded.

2. Serpentinite and Related Rocks :-

These rocks crop out in a moderate to high relief terrain. They exhibit different colours, green, violet and brown. The talc-carbonate rocks are well exposed at Gabal Um El Tuyur El Fugani.

3. Metagabbro :-

These are massive and greyish-green to dark green , dissected by irregular joints filled partly with quartz and carbonate matter.

4. Schistose Basic to Intermediate Metavolcanics and Related Pyroclastics :

They form moderate hills. They are dark greyish green with brownish weathered surface, sheared and slightly to moderately deformed. They are fine grained and nonporphyritic,frequently of mafic composition represented by metabasalts.

5. Schistose Intermediate to Acid Metavolcanics and Related Pyroclastics :

They form dark greyish green rocks in moderate relief. They are commonly hard, compact and sometimes porphyritic showing concoidal fractures. They are represented by meta- rhyolite,meta - dacite and rarely meta - andesite.

6. Tonalite & Granodiorite:

These rocks are the predominant rock type in the study area . They vary from whitish- grey to greyish black and are medium to coarse – grained, composed essentially of plagioclase, orthoclase, quartz and mafic minerals. They contain oval xenoliths of dioritic composition. They range from granodiorite to tonalites and are equivalent to the G1 granites of Hussein et al. (1982). They are cut by acidic and basic dykes, pegmatite and quartz veins.

7. Younger Gabbro :

It forms low to medium relief terrain and the rocks are hard, massive and weather into spheroidal blocks. The rock is banded and shows rythmic layering, and is medium to coarse grained, composed of plagioclase, pyroxene and hornblende with a considerable amount of iron oxides.

8. Alkali Feldspar Granite ;

It exhibits high to moderate relief and is characterized by forming rectangular masses with approximately equal dimensions. It is coarse to medium- grained, buff and composed essentially of alkali feldspar, quartz and minor biotite. It is jointed and exfoliated. This granite is equivalent to the G2 granites of Hussein et al. (1982).

ORE DEPOSITS AND OCCURRENCES

1. Quartz Veins :

Quartz veins are randomly distributed in the area. cutting through all its rock units.They extend for 10m to 200m, their thickness varies from 0.2 to 2m. The contact between the veins and the country rocks is usually marked by silicification, chloritization and sericitzation of the country rocks. The veins and veinlets of quartz are smoky, milky or white. The smoky veins trend NE- SW and are usually gold bearing.

2. Magnesite veins :

Magnesite veins, veinlets and stockworks are recorded traversing the serpentinite masses at Gabal Um El Tuyur El Tahtani; and Gabal El Adraq . They extend for up to 100m and are 5m thick. Fig.(2) shows stockwork of magnesite at Gabal El Adraq .

3. Chromite :

This ore occurs as lenses, 3m long and 20cm thick at Gabal El Adraq . Other chromite pods were observed at Gabal Um El Tuyur El Tahtani, their thickness is about 30cm and extend for about 1m (Fig.3).

4. Asbestos and Talc :

These occur in minor amounts at Gabal Um El Tuyur El Fugani .associated with the serpentinites and related rocks.

5. Ateration Zones :

They follow the fracture zones at Gabals El Adraq ; Um El Tuyur El Tahtani; Um El Tuyur El Fugani and Agret .The zone may be 300 m long and 20m wide.. Alterations are represented by chloritization, epidotization, sericitization, carbonatization and silicification.

<!--Gold Occurrences :

Three gold occurrences are known these are ;

a- El Hateib gold occurrence is located at the intersection of Lat. 22o 14` 10 and Long. 34 o 42` 30``). (Fig.4). Gold mineralization occurs as smoky quartz veins and veinlets, striking E-W. Their thickness ranges from few cm to 2m and the veins extend for about 10m to 200m along the strike.. The host rocks are schistose, fine grained, and dark metasediments. Their schistosity strikes E-W and dips Old tunnels , shafts, mills and ruins are present.

b- Um El Tuyur El Fugani gold occurrence lies at the intersection of Lat. 22o 18` 30`` and Long. 34o 38` 15``. Gold mineralization with abundant cubes of pyrite are related to smoky quartz veins, striking NE- SW, parallel to the schistosity of the host.metasediments(Fig 5).

c- Betam gold occurrence is represented by alteration zones at Lat. 22o 16` 15`` & Long. 34o 27` 30`` . The zone strikes NW- SE andcould be traced for 1000m and reaches up to 5m in thickness (Fig .6). The alteration zone is characterized by ferrugenation, carbonatization, silicification and associated quartz veins and veinlets. Worthy of remark that these gold occurrences were excavated and partly exploited for gold as shown in Fig.7

GEOCHEMICAL PROSPECTING

Regional geochemical prospecting on scale 1:100,000 was carried out in the study area. A total of 1218 stream sediment samples were collected.with a density of one sample for an area of 1km x 500m. Samples were collected from the upper 30cm and sieved to fraction 1 to 0.25 mm to have the silty clayey fraction. All samples were analyzed using spectrograph Zeiss Q- 24 for the trace elements Mn, Ti, Pb, Sn, W, Bi, Be, Nb, Mo, Cu, Ag, Ta, Zn, Ni, Co, Cr, V, Cd, Y, La, Zr, Ba and Sr byTheCentral Laboratories of EGSMA.

One- hundred- fifty lump samples, 5kg each, were collected from the alteration zones and quartz veins along geological prospecting traverses cross- cutting these veins and zones. Fifty- one samples with anomalous values from spectral analysis were checked for Au, Ag, Cu, Co, Ni, and Cr by the Atomic Absorption spectrophotometry “As Gbc- 908. Twenty- five samples, 0.03m3 each were collected for panning from pits more than 0.5m deep. The concenterates of ten panned samples contain grains of gold, so these samples were analyzed for gold by Atomic absorption and fire assay methods, to get a quantitative evaluation of the gold content.

RESULTS

Mineralogical Analysis

The mineralogical study of the alluvial samples revealed that the highly magnetic fraction is composed mainly of magnetite, while the moderately so is ilmenite. The weakly magnetic fraction is represented by amphiboles, feldspars and garnet with some geothite. The heavy crop from the non-magnetic fraction contains gold, zircon, rutile,monazite, fluorite and xenotime. Gold was recognized as 2, 3, 5, and 6 grains in 4 samples. It occurs in massive and dendritic shapes.

Dry Stream Sediment Sampling

The spectral data of 1218 samples were treated according to the statistical methods of analysis by Koch and Link (1970.) and Hutchison (1974). The essential parameters of the distribution (arithmetic mean, variance,standard deviation and threshold) were obtained (Table 1). The anomalous values for Cr and Ni (Table 1) are related to drainage crossing mainly serpentinite and metagabbro at Gabal El Adraq , Um El Tuyur El Tahtani and Um El Tuyur El Fugani. For copper anomalous values are related to tributaries crossing metasediments and metavolcanics at the south eastern part of the area rmapped. Vanadium values are related to drainage crossing the tonalite at the northeastern section of the investigated area. Barium and strontium are related to tributaries of Wadi Difiet. Zirconium values are related to tributaries of Wadi Rod El Bill crossing the granitic rocks at the north western part of the area.

Table (1) : Limit of detection, range, mean, standard deviation and anomalous values for dry stream sediment samples :

Element	Limit of	Range		mean	Standard	Threshold	Anomalous	Number
	detection	from	to	(W)	deviation (S)	(T3)	values	of samples
Cr	100	<100	10000	132	131	527	800-10000	37
Ni	10	<10	1000	45	56.2	213.2	400-1000	9
Cu	3	3	300	17.3	21	80.3	100-300	106
V	10	10	200	57	33.4	157.5	200	40
Zr	30	<30	1000	191	123	696	800-1000	23
Ba	100	100	2000	329	173	839	1000-2000	63
Sr	100	<100	1000	247	151	709	800-1000	30