The Influence of CO2 on the Solubility of Quartz in Single-Phase Hydrothermal Fluids: Implications for the Formation of Stockwork Veins in Porphyry Copper Deposits
The Influence of CO2 on the Solubility of Quartz in Single-Phase Hydrothermal Fluids: Implications for the Formation of Stockwork Veins in Porphyry Copper Deposits
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DOI：
10.5382/econgeo.4680
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发表时间：
2019-09
期刊：
影响因子：
5.8
通讯作者：
T. Monecke;Jochen Monecke;T. J. Reynolds
中科院分区：
文献类型：
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作者：
T. Monecke;Jochen Monecke;T. J. Reynolds
斑岩铜矿由低品位网脉和浸染状硫化物带组成，其中含有热液系统演化过程中形成的特征脉代。本文研究了在温度为150° C至550°C、压力为100至2，000 bar、CO2浓度不超过8 mol %的条件下，CO2浓度变化对形成斑岩矿床网脉的单相热液中石英溶解度的影响。计算表明，石英在热液流体中的溶解度随CO2含量的增加而降低。逆石英溶解度在含CO2流体中不太明显，并且在CO2浓度超过6mol%的单相流体中未观察到。尽管有CO2的影响，退石英溶解度在斑岩网脉的形成中起着重要的作用，其中包含很少或没有石英作为脉石mineral.In高温和岩石静压力条件下低于900巴，早期黑云母脉可以形成作为单相热液流体的条件下的退石英溶解度或近恒定的石英溶解度的准等压冷却的结果。由辉铜矿或不含石英的深成硫化铜矿组成的网脉可在高达450°C的温度和约250至900巴的静水压力下形成。在CO2的存在下，逆行石英溶解度在恒定压力下向稍低的温度移动。在低于375°C的温度下，石英在准等压冷却过程中沉淀，而不管热液流体中的CO2含量如何，从而形成晚期斑岩石英脉。
Porphyry copper deposits consist of low-grade stockwork and disseminated sulfide zones that contain characteristic vein generations formed during the evolution of the hydrothermal systems. The present contribution examines the influence of variable CO2 concentrations on the solubility of quartz in single-phase hydrothermal fluids forming stockwork veins in porphyry deposits at temperatures of 150° to 550°C and pressures ranging from 100 to 2,000 bar at concentrations up to 8 mol % CO2. The calculations demonstrate that quartz solubility in hydrothermal fluids decreases with increasing CO2 content. Retrograde quartz solubility is less pronounced in CO2-bearing fluids and is not observed in single-phase fluids having CO2 concentrations exceeding 6 mol %. Despite the effects of CO2, retrograde quartz solubility plays an important role in the formation of porphyry stockwork veins that contain little or no quartz as a gangue mineral. At high temperatures and lithostatic pressure conditions below 900 bar, early biotite veins can form as a result of quasi-isobaric cooling of single-phase hydrothermal fluids under conditions of retrograde quartz solubility or near-constant quartz solubility. Stock-work veins consisting of molybdenite or hypogene copper sulfide minerals lacking quartz could form at temperatures of up to 450°C under hydrostatic pressures ranging from ~250 to 900 bar. In the presence of CO2, retrograde quartz solubility is shifted toward slightly lower temperatures at constant pressure. At temperatures below ≾375°C, quartz is precipitated during quasi-isobaric cooling irrespective of CO2 content of the hydrothermal fluids, resulting in the formation of late porphyry quartz veins.