Titanium-oxide activity during the formation of gold-bearing quartz veins: evidence for closed system behavior
Abstrakt
Titanium contents of both vein and magmatic quartz from five Bohemian gold deposits with known P-T history were used to calculate/discuss the titanium oxide activities (a(TiO2)) of natural quartz formed in the absence of Ti-buffering phases at 250-550 °C and 0.1-4 kbar. Data suggest significant variations in a(TiO2) during vein quartz formation, due to variation of P, T and growth rate.
Negative correlation between a(TiO2) 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 ascending fluid with surrounding rocks). We propose a relationship for quantifying disequilibritun quartz formation that can be readily applied to quartz with known P-T history.
The relationship was tested on natural samples exhibiting both rapid and slow crystallization. An example of extreme Ti enrichment (up to approx. 30 x) in quart, associated with its rapid growth, is described and discussed.