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Council for Geoscience (CGS) has carried out a semiregional geochemical survey of the Tugela Terrane, in KwaZulu-Natal, which has resulted in the delineation of several new target areas for follow-up studies and a few geological anomalies near to known mineral occurrences, which warrant re-examination. The Tugela Terrane is predominantly composed of supracrustal rocks with a potential for gold and base metal mineralisation. Speaking at the recent 2016 CGS conference, in Tshwane, CGS geo- logist Mehdi Bensid informed delegates that, in total, 11 321 soil samples, each weighing 5 kg, were collected from a depth of 20 cm on a 500 × 500 m grid. He said the samples were dried, sieved and analysed by means of X-ray fluorescence spectro- metry for mineralisation at the CGS laboratory, in Tshwane. The samples were also analysed by the Henan Institute of Geological Survey at its geoanalysis laboratory in Henan, China.
Bensid commented that the results of all elements, including relevant multi-element groups, were plotted on distribution maps using the cloud-based mapping platform ArcGIS. “From the maps, target areas for gold, chromium, nickel, cobalt, copper, zinc, lead, arsenic and rare-earth elements (REEs) were identified, evaluated and listed as potential targets for future follow-up work,” he highlighted. The gold targets were subdivided into primary- source-type and secondary-placer-type target areas. The most prospective auriferous placer target areas are downstream from the Ngubevu Phoenix and Mfongosi goldfields along the Tugela River Valley. Target areas at Central Nsuze and Melmoth goldfields were also identified. Bensid, moreover, noted that primary source gold anomalies earmarked for further investigation included the 20-km-long Ngubevu-Mfongosi trend, which was marked by several anomalies. He said that gold-plus-type anomalies around the iThuma area were expected to be exhalative-type deposits (sedimentary or volcanic) coinciding with east-west shear zones.
Bensid pointed out that the chromium-nickel- copper-gold trend prevalent in the Tugela Rand Ultramafic Complex also required further investigation. “Possible shear-hosted mineralisation east of the Nkuzana mountains, in KwaZulu-Natal, may follow anomalous trends that are less well defined but strongly supported by gold.” Further, he remarked that target areas for chromium and nickel that might warrant further investigation included the anomalies surrounding the Sithilo Ultramafic Complex within the Tugela Terrane.
Bensid said that these anomalies were all considered to be chromium targets since only chromium mineralisation had been reported in the Sithilo Complex, while the lack of anomalous copper support reduced the likelihood of nickel and copper sulphides in these rocks. Additionally, he stated, copper/lead/zinc anomalies deserving further investigation included the Mfongosi copper/lead/zinc anomaly, which corresponded to an “important gold trend” in the area and represented a “truly multielemental anomaly.” “The alkali-element and REE target areas, which deserve further investigation, include those in the leucrocratic biotite granite as possible sources. The Halambu Gneiss and the Bulls Run Complex of the Tugela Terrane should also be explored as possible sources of alkali elements and REEs in general,” Bensid concluded.
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