Abstract

Oscillatory zoning in tennantite-(Fe) crystals found in carbonate–sulfide aggregates at the Darasun gold deposit has been studied. Similar elements have been distinguished in zoned crystals: core, “identical oscillatory rhythm,” rhythms with crystallographic and wavy oscillatory zoning, and rim with poorly defined fine oscillatory zoning. Oscillatory zoning is due to considerable variations in the contents of semimetals (As and Sb) and formally divalent metals (Fe and Zn). Variations in As and Sb are coupled with changes in Fe and Zn, respectively. Both As and Fe contents increase in zoned crystals from the center to the edge: Sb/(Sb + As) ratio varies from 0.44 to 0.03, while Fe/(Fe + Zn) ratio varies from 0.38 to 0.75. The evolution of the composition of zoned tennantite-(Fe) crystals is similar to that of the fahlore at the deposit and to that in pseudomorphic rhythmically zoned tennantite aggregates. A negative relationship between Sb/(Sb + As) and Fe/(Fe + Zn) ratios has been revealed: it is stronger in the internal rhythms than in the external. The oscillatory zoning formed under conditions close to local equilibrium under the influence of external factors at the early crystal growth stages. The composition of zones reflects (random) fluctuations of the external parameters caused by variations in physicochemical conditions (T, fS₂, fO₂, and pH) and fluid composition, by fluid boiling or mixing of fluids from different sources. Subsequently, changes in the crystal morphology, irregular fluctuations in crystal compositions, and various trends in the behavior of components were caused by the appearance of a concentration gradient at the mineral–fluid boundary and kinetic phenomena on the mineral growth surface. The zoning developed under the influence of “internal” mechanisms under conditions far from equilibrium due to the interrelation between the growth of zones enriched in one component, resulting from the concentration gradient at the crystal–fluid boundary, and the incorporation of another component, in particular, as a result of the self-organization process uninfluenced by external factors. It has been concluded that the oscillatory zoning in fahlore is caused by the difference in solubility of the end-members of the tennantite–tetrahedrite solid solution due to changes in the metal and semimetal migration conditions with a decrease in temperature and fluid salinity. Hence, the oscillatory zoning in tennantite-(Fe) crystals at the Darasun deposit was related to self-organization processes complicated by random fluctuations (noise) of the external parameters.

中文翻译：

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达拉孙金矿（俄罗斯东贝加尔湖地区）的天南铁矿-（铁）振荡带

摘要

已经研究了在Darasun金矿床的碳酸盐-硫化物聚集体中发现的钙铁矿（铁）晶体的振荡区带。在分区的晶体中已区分出类似的元素：核心，“相同的振荡节律”，具有晶体学和波浪形振荡分区的节律，以及具有定义不清的精细振荡分区的边缘。振荡区带是由于半金属（As和Sb）和形式上为二价金属（Fe和Zn）含量的显着变化所致。As和Sb的变化分别与Fe和Zn的变化有关。从中心到边缘，带状晶体中的As和Fe含量均增加：Sb /（Sb + As）比从0.44到0.03变化，而Fe /（Fe + Zn）比从0.38到0.75变化。分区的钙长石-（Fe）晶体的组成演变与沉积处的辉石和假晶状有节奏的分区的钙钛矿聚集体的演化相似。Sb /（Sb + As）与Fe /（Fe + Zn）比之间存在负相关关系：内部节奏比外部节奏更强。在早期晶体生长阶段，在外部因素的影响下，在接近局部平衡的条件下形成了振荡分区。区域的组成反映了由理化条件变化引起的外部参数的（随机）波动（T，在早期晶体生长阶段，在外部因素的影响下，在接近局部平衡的条件下形成了振荡分区。区域的组成反映了由理化条件变化引起的外部参数的（随机）波动（T，在早期晶体生长阶段，在外部因素的影响下，在接近局部平衡的条件下形成了振荡分区。区域的组成反映了由理化条件变化引起的外部参数的（随机）波动（T，f S ₂，f O ₂和pH）和流体成分（通过流体沸腾或混合不同来源的流体）。随后，晶体形态的变化，晶体组成的不规则波动以及组分行为的各种趋势是由于在矿物-流体边界上出现浓度梯度和矿物生长表面上的动力学现象而引起的。在远离平衡的条件下，在“内部”机制的影响下形成了分区，这归因于富含一种组分的区域的生长之间的相互关系，这种富集是由于晶体-流体边界处的浓度梯度导致的，而另一种组分的掺入则导致了。特别是由于不受外部因素影响的自组织过程。已经得出结论，由于金属和半金属迁移条件的变化以及温度和流体盐度的降低，钙钛矿-四面体固溶体末端成员的溶解度差异导致了fahlore中的振荡区带。因此，Darasun矿床中的辉长岩-（Fe）晶体的振荡分区与自组织过程有关，该过程由于外部参数的随机波动（噪声）而变得复杂。