Abstract
Quartz is the most common gangue mineral in hydrothermal veins. Coupled with capacities of hosting fluid inclusions and recording varieties of microtextures, its solubility behavior may provide unparalleled insights into hydrothermal processes. In this study, the Linglong goldfield in Jiaodong is targeted to investigate gold-producing quartz veining process. Scanning electron microscope (SEM)-cathodoluminescence (CL) imaging uncovered three episodes of quartz deposition, intervened by an episode of quartz dissolution. Based on newly-developed quartz solubility diagrams and CL-aided fluid inclusion microthermometry, it is proposed that precipitation of the earliest quartz (Qz1) was controlled by CO2 content increase and subordinately affected by decompressional cooling, leading to the formation of the early thick gold-barren veins (V1); the second generation of quartz (Qz2a) was formed by the same fluids that may have been diluted and cooled by meteoric water, leading to a greatly reduced quantity of quartz and the deposition of pyrite and gold; and the third generation of quartz (Qz2b) was deposited along with polymetallic sulfides, due to fluid cooling following a quartz dissolution event likely induced by cooling in retrograde solubility region and/or CO2 content decrease. This research may elucidate gold formation processes in orogenic intrusion—related deposits, and points to imperative CL-based in situ analyses for future studies.
Highlights
Quartz is the most important silica mineral and widely occurs in igneous, metamorphic, sedimentary and hydrothermal rocks of the Earth’s crust
Quartz solubility analysis has been much less employed in the studies of orogenic intrusion-related gold deposits, leading to less knowledge of the veining processes that are responsible for gold deposition
Quartz from the four types of vein are examined by Scanning electron microscope (SEM)-CL imaging, and the microtextures are used as petrographic guidance for constructing mineral paragenesis and quartz sequence, and for guiding fluid inclusion petrography
Summary
Quartz is the most important silica mineral and widely occurs in igneous, metamorphic, sedimentary and hydrothermal rocks of the Earth’s crust. Highly complex veining processes involving the deposition, dissolution, reopening, recrystallization and overgrowth of quartz and incursion of cooler and dilute meteoric waters have been discovered [8,15] These pieces of information shed lights on where cupriferous fluids are sourced and how these fluids precipitate metal sulfides and quartz. H2 O-NaCl-CO2 ternary system, but data are only available for the single-phase region This lack of data for two-phase field poses a challenge for thoroughly understanding vein formation processes in orogenic intrusion-related setting, since fluid immiscibility is quite common and is considered a critical factor for gold genesis [19]. Based on a methodological combination of CL petrography, fluid inclusion and newly-developed quartz solubility diagrams that cover both the single-phase and the two-phase field, this study elucidates veining processes in this deposit, which has implications for understanding quartz deposition and dissolution processes in a wide range of geological settings
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