Zonation in primary geochemical haloes for orogenic vein-type gold mineralization in the Quartz Ridge prospect, Sukari gold mine area, Eastern Desert of Egypt

Abstract

The Quartz Ridge prospect is one of >100 gold occurrences distributed in the Neoproterozoic basement rocks of the Eastern Desert of Egypt. The mineralization is hosted in quartz veins along NE-trending shear zones, and their associated altered wallrocks. Opaque minerals include pyrite and arsenopyrite with less abundant chalcopyrite, galena, and sphalerite. Gold occurs as tiny inclusions and as microfracture-filling grains mainly in arsenopyrite and in deformed quartz. Sericitization, carbonatization, and silicification are the main alteration signs accompanying ore formation. The chemical analysis of 640 core samples from four selected boreholes from the study area was used for characterizing the primary geochemical haloes and their zonation developed around detected subsurface mineralized zones. Statistical analysis of the geochemical data applying techniques based on median absolute deviation (MAD) values and log-ratio transformation (CLR) was carried out to address the problems of outliers and closed compositional data, whereas statistical factor analysis (FA) combined with enrichment factor (EF) associations were used to investigate the multi-element associations describing the gold mineralization and its primary dispersion haloes. Mineralization (Au-Ag-As-Sb ± S), alteration (Ba ± Cu ± Mo) and wall rock (Ni-Cr ±Co) associations can be inferred directly by factor analysis study. However, the dispersion of trace elements around mineralized zones can better be described by their enrichment factors calculated for data subsets. More than one stage of hydrothermal activity has been suggested and believed to be responsible for precipitating ore metals and their associated elements. Molybdenum and copper were found to be good indicators for upper zones, while tungsten and zinc are good indicators for the lower or down-dip zones. The current study manifests the success of using statistical procedures based on data transformation for compositional data analysis (i.e. centered log-ratios) coupled with enrichment factors in characterizing the primary geochemical haloes and their zoning which can be effectively used to follow similar occurrences of orogenic hydrothermal gold deposits.