Mineralogical and geochemical studies of some witwatersrand gold ores with special reference to the nature of the phyllosilicates

[摘要] The present thesis is divided into three parts. The study describedin Part I arose out of a request by the Chamber of Mines Mining ResearchLaboratory to the National Institute for Metallurgy to undertake a preliminarystudy of whether it would be feasible, in Witwatersrand conglomerates, to carryout rapid delimitation of areas rich in gold and/or uranium at the rock face, aprocedure which would permit areas of rich ore to be removed selectively bymeans of the rock-cutter. The approach adopted in this study was essentiallygeochemical, while conventional mineralogical techniques (macro-auto radiographs ,thin section and polished section analyses) provided a control. The samples weredrawn from the Vaal Reef at Hartebeestfontein and Zandpan and from the VentersdorpContact Reef at Venterspost, and were analysed quantitatively for gold, silver,uranium, pyrite, muscovite, pyrophyllite, chlorite, quartz, iron, potassium,nickel, titanium, zirconium and chromium. The intensity of the interrelationshipsbetween the elements and minerals analysed for was examined statisticallyby means of correlation covariance and factor analysis programmes written foran IBM 360/50 digital computer. A sympathetic relationship -- defined as significantpositive correlation (with a correlation coefficient r> 0. 7) -- was found toexist between gold and uranium in both the Vaal Reef and Ventersdorp ContactReef samples. These findings suggest that gold and uranium can be removedSimultaneously by means of the rock-cutter, and that radioactivity can be used asan indicator for on-site delimitation of areas rich in gold.In the course of the study described in Part I, it became evidentthat little detailed mineralogical work had ever been done on the phyllosilicatesoccurring in the Witwatersrand System. Accordingly, certain phyllosilicatesfrom Witwatersrand conglomerate bands and other sources were examined in detail,this study being described in Part II of the present thesis. This study calledfor detailed chemical, optical, X-ray crystallographic, infra-red, differentialthermal and thermogravimetric analyses, the results of which are presented. Thefindings were examined in the light of variolls classification schemes that havebep proposed for the phyllosilicates. This investigation revealed the need for auniversally acceptable system of classification for the phyllosilicates, whichshould preferably be drawn up under the auspices of the International MineralogicalAssociation to avoid the confusion that exists at present.Part III of the present thesis is devoted to a discussion and descriptionof various analytical techniques that had to be modified or developed to meetth8 requirements of the studies described in Parts I and II. The techniques describedinclude:(1) An X-ray diffraction method which was developed for the quantitativeanalysis of pyrite, muscovite, pyrophyllite, chlorite and quartz in crushed orefrom Witwatersrand conglomerates. This method makes use of novacul iie as anexternal standard and of binary mixtures as analytical standards, and had a meanabsolute error of 1. 1 %. This method may be expanded to permit analysis of ann-component mixture.(2) A whole rock pressed powder technique of X-ray fluorescenceanalysis which was used for the quantitative determination of iron, potassium,nickel, titanium, zirconium and chromium. This method makes use of internstionalrock standards as external standards.Six computer programmes used for the computation of the analyticalresults and in the statistical and crystallographic calculations are alsopresented in Part III.

[发布机构] University of the Witwatersrand