重砂分级-扫描电镜-能谱等技术研究湖南张家界黑色页岩贵金属元素赋存状态

黑色岩系是多种有用元素的重要载体,Cu、Pb、Zn、Ni、Mo、V、U、Au、Ag、稀有和稀土元素在黑色岩系中异常富集,某些黑色岩系的贵金属(铂族元素、Au、Ag)也异常富集,其含量甚至部分超过了基性和超基性岩,这类黑色页岩矿床中铂族元素(PGEs)的赋存状态至今尚未有一个确切的定论。本文采集了湖南张家界属寒武系牛蹄塘组黑色页岩中Mo-Ni矿层作为研究样品,通过化学分析表明矿石中含Pt 531×10~(-9),Pd 514×10~(-9),Os 185×10~(-9),PGEs合量为1259.43×10~(-9),Au 332×10~(-9),Ag 12.2×10~(-6),已富集成矿。进一步利用重砂分级、化学分析、X射线衍射、扫描电镜及能谱技术研究了贵金属元素赋存状态,结果表明:①Ag:主要以独立矿物形式存在,少量以类质同象形式赋存在其他矿物中。独立矿物有砷铜银矿、硫锑铜银矿、硫锑铅银矿、锑银矿、硫银锡矿、硫砷银铅矿、银黄锡矿、辉银矿、锑-银-锡互化物;类质同象主要是银黝铜矿-银砷黝铜矿、含银方铅矿和含银砷铜矿等。②Au:未发现独立矿物,黄铁矿是重要载金矿物。③PGEs:未见独立矿物,在不同重砂分级样品中没有富集,具分散性,推测铂族矿物很可能是以纳米形式存在,建议今后研究选矿工艺时,可考虑从制取纳米材料的思路进行应用研究。本文Ag-Sn-Sb互化物的发现为研究黑色岩系多元素富集成因机制提供了重要物证。

Study on Occurrence of Noble Mental Elements in Black Shale Series in Zhangjiajie, Hunan Province by Heavy Placer Classification-SEM-EDS and Other Techniques

BACKGROUND: Black shale series is an important carrier of many useful elements. Cu, Pb, Zn, Ni, Mo, V, U, Au, Ag, rare and REE elements were abnormally enriched in the black rock series. The noble metal elements (PGE, Au, Ag) in some black shale series are also anomalously enriched, even partially exceeding the basic and ultrabasic rocks. However, the occurrence of PGE in such black shale series is still an unsolved problem.
OBJECTIVES: In order to clarify the occurrence of noble metal elements, Mo-Ni deposits in the black shale of the Niutitang Formation of the Cambrian system in Zhangjiajie, Hunan Province, were collected as research samples.
METHODS: The heavy placer classification, chemical analysis, X-ray diffraction analysis, scanning electron microscopy and energy disperse spectroscopy were used to study the occurrence of noble metal elements.
RESULTS: Chemical analysis showed that:Pt 531×10^-9, Pd 514×10^-9, Os 185×10^-9, PGEs 1259.43×10^-9, Au 332×10^-9, Ag 12.2×10^-6. These precious metals were concentration in ore-formation.
CONCLUSIONS: 1) Silver exists mainly as independent minerals, a small amount exist as isomorphism in other minerals. Independent minerals include:novakite, polybasite, andorite, dyscrasite, canfieldite, marrite, hocartite, argentite, Ag-Sn-Sb intergrowth compounds. The isomorphism is mainly freibergite-Ag-tennantite, silver-bearing galena and silver-bearing domeykite. 2) Native gold doesn''t exist as independent mineral and is also not adsorbed by carbon. Meanwhile, pyrite was an important gold-bearing mineral. 3) PGEs do not exist as independent minerals and are no longer enrichment in different classification sample. It is speculated that PGE minerals are likely to exist in nanometer form. It is suggested that the application of nanomaterials can be considered in the future study of mineral processing.