Abstract

Heterogeneous rhythmic–zonal aggregates of tennantite-IV partly or completely replacing early homogeneous Zn-tetrahedrite-I grains and euhedral (Fe–Zn)-tennantite-I crystal were found in ores of the Darasun gold deposit. The different stages of fahlore replacement were observed. This initiates at grain boundaries and is terminated by a complete transformation into pseudomorphic, newly formed (Zn–Fe)-tennantite-IV aggregates surrounded by Zn-tetrahedrite-IV. These aggregates closely associate with bournonite and galena, and their precipitation initiated the formation of pseudomorphs. As is evident from the results of EMPA, (Fe–Zn)-tetrahedrite enriched in As in relation to Zn-tetrahedrite-I was precipitated at the initial stage. Tennantite with wide variations in the Sb/(Sb + As) and Fe/(Fe + Zn) ratios predominates in zonal heterogenous aggregates. There is a negative correlation between Sb/(Sb + As) and Fe/(Fe + Zn) ratios in (Fe–Zn)-tetrahedrite–tennantite-IV. In all sites, there is a miscibility gap between As and Sb and a sharp decrease in Sb/(Sb + As) ratio and increase in Fe/(Fe + Zn) ratio at the contact between Zn-tetrahedrite-I and newly formed (Fe–Zn)-tetrahedrite–tennantite-IV. The sharp zigzag boundaries between Zn-tetrahedrite-I and tennantite-IV and pores in newly formed aggregates provide evidence for coupled dissolution–precipitation reactions. The dissolution was initiated by disequilibrium between Zn-tetrahedrite-I and undersaturated fluid due to the precipitation of galena and bournonite. The precipitation of tetrahedrite–tennantite-IV occurred under the conditions of oscillation in Sb/(Sb + As) and Fe/(Fe + Zn) ratios due to the gradient of concentrations in the fluid. The temperature of crystallization of zonal heterogenous tennantite-IV aggregates ((134–161) ± 20°С) was calculated by the sphalerite–fahlore geothermometer. Instability of early Zn-tetrahedrite-I results from hydrothermal fluid cooling, decrease in fluid salinity, and change in the tetrahedrite and tennantite solubility due to the evolution of the conditions of semimetal migration.

中文翻译：

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达拉孙金矿（俄罗斯东贝卡卡利亚）中的辉长岩-四面体矿物的溶解-沉淀反应

摘要

在Darasun金矿中发现了部分或完全替代早期均一的Zn-四面铁矿-I晶粒和正方（Fe-Zn）-tennantite-I晶体的球粒IV的异质节律-带状聚集体。观察到了不同的fahlore替换阶段。这始于晶界，并通过完全转变成被Zn-四面体-IV包围的新形成的假晶（Zn-Fe）-钙钛矿-IV聚集体而终止。这些聚集体与针铁矿和方铅矿紧密结合，它们的沉淀引发了假晶形的形成。从EMPA的结果可以明显看出，相对于Zn-四面体-I，富含As的（Fe-Zn）-四面体在初始阶段析出。在带状异质骨料中，Sb /（Sb + As）和Fe /（Fe + Zn）比率变化很大的Tennantite占主导地位。在（Fe-Zn）-四面体-球铁矿-IV中，Sb /（Sb + As）与Fe /（Fe + Zn）之比之间呈负相关。在所有位置，As与Sb之间都存在可混溶的间隙，并且在Zn-四面体I与新形成的（I）接触时，Sb /（Sb + As）比急剧下降，而Fe /（Fe + Zn）比增加。 Fe-Zn）-四面体-球铁矿-IV。锌-四面体-I和钙云母-IV之间的尖锐的锯齿形边界以及新形成的聚集体中的孔为耦合的溶解-沉淀反应提供了证据。溶解是由于方铅矿和钙锌矿的沉淀，导致锌-四面体-I与欠饱和流体之间的不平衡而开始的。由于流体中浓度的梯度，在振荡条件下，Sb /（Sb + As）和Fe /（Fe + Zn）比出现了四面体-钙云母-IV的沉淀。用闪锌矿-fahlore地热计计算了带状异质囊状IV-IV聚集体的结晶温度（（134–161）±20°С）。早期Zn-四面体-I的不稳定性是由于水热流体冷却，流体盐度降低以及由于半金属迁移条件的演化而导致的四面体和球粒体溶解度的变化所致。