Geochemical Prospecting For Gold In Umm Saqata-Qala En Nahal Region, Gedarif State, Sudan

Abstract

A loW density stream sediments survey has been conducted in Umm Saqata- Qala En Nahal areas (about 2450 Kmz), Gedarif State — Eastern Sudan. The aim of the study is to prospect for gold and associated elements using a most cost and time effective exploration method, in a low grade none explored Pan- African volcano-sedimentary greenstone belt. Geologically Umm Sagata-Qala En Nahal areas consist of Ophiolitic Complex, structurally overlying a layered sequence of low-grade volcano-sedimentary units. Syn- to late and post-orogenic granitoid complexes intruded the above- mentioned sequences. Two generations of quartz veins have been observed associated with syn- and post-orogenic magmatic events. An orientational study has been conducted to determine the optimum fraction (grain size) for sampling in a rich Savana zone. About l2 samples have been collected fiom a mineralized locality and sieved for -125 um and — 63 um. Both of the fractions have been analyzed for gold using wet chemical technique with detection limit 2 ppb. Trace elements have been determined using Aque- regia - ICP technique. Concentrations of gold mineralization and associated elements are typically found in the finest grain size fraction (-63 um). The background and threshold values for gold in stream sediments were chosen 9.39 ppb and 45.6 ppb respectively after evaluation of the geochemical data. As it is the first time to conduct such survey in the study area a number of gold anomalies" have been recorded. After selecting the right fraction, the Umm Saqata — Qala En Nahal areas have been fully geochemically surveyed at a density of 1 sample per 10 Kmz. A total of 196 samples have so far been collected fi'om first, second and third order streams of the drainage system for low density geochemical survey. The analytical data are evaluated using Univariate Analyses (statistical parameters, histograms, cumulative frequency curves and geochemical parameters) and Multivariate Analyses (correlation coefficient, regression analysis, factor analysis and cluster analysis). The distribution of gold mineralization in stream sediments is erratic. It is evident that most of the samples with high anomalous content espatially occur in Umm Saqata-Qala En Nahal areas related to the metavolcano- sedimentary sequences which are injected by quartz veins of the first generation. Some localities are clearly structurally controlled as indicated by gold occurrences at or near regional Shear zones along NW — SE trend. positive correlation exists between Au and" trace elements Ag, As, Bi, Cd, Co, Cr, Cu, Fe, Ge, Mn, Nb, Ni, Sb, Se, Sn, Ta, U and W. Correlation between Cu, Zn and As may indicate presence of sulphide minerals in stream sediments.