Diagnostic fluid inclusions of different types hydrothermal gold deposits 论文

摘要

This paper,using gold deposits as example,attempts to setup a scientific linkage between ore geology and fluid inclusions,considering that in previous published works,observations and measurements of the fluid inclusions commonly were not well interpreted.In some cases,geological data did not agree with the results obtained from fluid inclusion studies.In this paper,we first review previous classifications of gold deposits,and then,subdivide gold deposits into five classes,based on the dominant ore-forming processes:1)intrusion-related hypothermal systems,such as porphyry-systems,breccia-pipes,IOCG and skarns;2)orogenic-or metamorphic hydrothermal type;3)epithermal-type,i.e.reworking hydrothermal deposits hosted in continental-facies volcanic- subvolcanic rocks;4)fine-grain disseminated type(Carlin-type and/or Carlin-style),i.e.reworking hydrothermal deposits hosted sediments;and 5)hydrothermal metalliferous sediments related to submarine venting,such as VMS and SEDEX styles.In this work we select diagnostic geological and fluid-inclusion characteristics of these five classes of ore-systems,and clarify their key differences that can be used as genetic markers.Ore-fluids are classified into three end-members,namely reworking,metamorphic and magmatic fluids.Many ore-systems are known to form as a result of multiple fluids during multi-stage events;and their late-stage of mineralization always being caused by fluids with a high-proportion of reworking of the original ore systems or by renewed fluid flow. Therefore,the features of late-stage fluids,alteration and mineralization cannot be used to identify the origin and genetic type of an ore- system.Instead,we suggest that only the early-stage signatures can be employed to determine the origin and type of an ore-system. Reworking fluids are characterized by low-temperature(300℃),low-salinity and low-content of CO_2,and sourced from meteoric and/or sea water;metamorphic fluids by moderate-temperature,low-salinity and high-content of CO_2;and magmatic fluids by high- temperature,high-salinity and high-content of CO_2.Magmatic hydrothermal ore-systems contain multi-daughter-crystal-bearing and high-salinity,CO_2-rich fluid inclusions;metamorphic ore-systems contain low-salinity,CO_2-rich fluid inclusions;and the reworking hydrothermal ore-systems contain neither daughter-crystal-bearing nor CO_2-rich/bearing fluid inclusions,but are populated by aqueous water-solution fluid inclusions.Finally,we discuss the tectonic settings of the ore-systems of the various classes.For examples,the orogenic-type formed during processes of crustal compression,orogenesis,metamorphism and uplift;submarine metalliferous sediments developed in the setting of rift basins;Paleozoic or earlier epithermal-type ore-systems can be preserved in accretionary orogens.It is suggested that the ore-systems and their fluid inclusions can be used as an ideal probe to trace geodynamic evolution of continents.