Study of occurrence states and precipitation mechanism of tellurium in Huangtun Au -Cu -bearing breccia pipe in Luzong Basin, Anhui, eastern China

摘要

The breccia pipe -hosted gold ( copper) deposits are an important type of gold deposits, which are often accompanied by the critical metal tellurium mineralization. However, studies on the distribution and allocational characteristics and the precipitation mechanism of the tellurium in this type deposit are still weak. The Huangtun deposit is the most typical breccia pipe-hosted gold-copper deposit discovered in the Middle-Lower Yangtze River Valley Metallogenic Belt in recent years, accompanied by a large amount of telluride. Based on detailed field geological work and petrographic observations, this paper discovers a significant enrichment of tellurium in the deposit. Through whole-rock and micro-area geochemical analyses on different alteration types of ore and main tellurium-rich minerals in the Huangtun deposit, the distribution and allocation characteristics of the tellurium were clarified, and the precipitation mechanism of the tellurium was preliminarily discussed. The mineralization stages of the Huangtun deposit can be divided from early to late into sodium-calcium silicate, potassium silicate, chlorite-carbonate and illite-montmorillonite stages, forming corresponding alteration zones at different depths, and developing different intensities of gold and copper mineralization. The accompanying tellurium reserves of the Huangtun deposit are about 118. 71t, with an average grade of 5. 3g/t, reaching a medium scale and possessing significant integrated utilization value. Among them, potassium silicate altered ore is the main tellurium -rich ore, accounting for about 92. 37% of the total reserves with an average grade of about 9. 6g/t. About 89% to 99% of the tellurium in potassium silicate altered ore exists as independent minerals, mainly micron-sized and nano-sized tellurobismuthite inclusions distributed in pyrite, and the remaining part is in the form of isomorphs in pyrite and chalcopyrite. The sharp drop of the fluid temperature caused by decompression boiling leads to the sulfide precipitation, while the boiling process releases a large amount of gaseous H2S, and these two processes result in an increase in the f(Te-2)/f( S-2) ratio of the fluid. This may be the main mechanism for tellurium precipitation and enrichment in the Huangtun deposit.

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