Titanium-oxide activity during the formation of gold-bearing quartz veins: evidence for closed system behavior

[摘要] Titanium contents of both vein and magmatic quartz from five Bohemian gold deposits with known P–T history wereused to calculate/discuss the titanium oxide activities (aTiO2) of natural quartz formed in the absence of Ti-bufferingphases at 250–550°C and 0.1–4 kbar.Data suggest significant variations in aTiO2 during vein quartz formation, due to variation of P, T and growth rate. Negative correlation between aTiO2 and quartz formation temperature was documented for intrusion-related gold deposits,implying quartz precipitation under closed-system conditions (i.e., without substantial equilibration of the ascendingfluid with surrounding rocks). We propose a relationship for quantifying disequilibrium quartz formation that can bereadily applied to quartz with known P–T history. The relationship was tested on natural samples exhibiting both rapidand slow crystallization. An example of extreme Ti enrichment (up to ~30×) in quartz, associated with its rapid growth,is described and discussed.

[学科分类] 自动化工程

[关键词] thermobarometry;gold;quartz veins;titanium;Bohemian Massif