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Geology and ore-forming fluids of the Dayingezhuang gold deposit, Jiaodong Peninsula, eastern China: Implications for mineral exploration.

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Title: Geology and ore-forming fluids of the Dayingezhuang gold deposit, Jiaodong Peninsula, eastern China: Implications for mineral exploration.
Authors: Chai, Peng1 (AUTHOR) cx001chaipeng@163.com, Zhang, Hong-rui1 (AUTHOR) zhanghr@yeah.net, Dong, Lei-lei1 (AUTHOR), Zhang, Zhi-yu1 (AUTHOR)
Source: Journal of Geochemical Exploration. Sep2019, Vol. 204, p224-239. 16p.
Subjects: Gold ores, Prospecting, Quartz, Geology, Fluid inclusions, Fault zones, Fluid pressure
Geographic Terms: China
Abstract: The Dayingezhuang deposit is a representative large gold deposit within the Zhao-Ping fault zone in Jiaodong Peninsula, eastern China, and contains gold reserves of 170 t with an average grade of 3.10 g/t. The orebodies are hosted in the Late Jurassic Linglong granite intrusion and are Jiaojia-type (disseminated- or stockwork-style) ores. Mineralization and alteration are structurally controlled by the NE- to NNE-striking Linglong detachment fault located near the central section of the regional Zhao-Ping fault zone. Mineralization can be divided into primary and supergene periods. The primary period can be further divided into four hydrothermal stages: I) pyrite–(K-feldspar)–sericite–quartz; II) auriferous quartz–pyrite; III) quartz–gold–polymetallic sulfides; and IV) quartz–carbonate. Gold was mainly deposited in the second and third stages. Three types of fluid inclusion were observed (in decreasing order of abundance): AC-type (aqueous–carbonic), A-type (aqueous), and PC-type (pure carbonic). Based on petrographic, microthermometric, and laser Raman spectroscopic analyses of these fluid inclusions, three types of fluid inclusion assemblage (FIA) were identified in the quartz grains: FIA1 (AC- and PC-type), FIA2 (AC-, PC- and A-type), and FIA3 (A-type). First stage quartz grains contain mainly FIA1-type inclusions, with trapping temperatures of 305–388 °C and salinities of 4.28–8.51 wt% NaCl equivalent. Quartz grains that formed in the second and third mineralization stages contain all three types of FIA. Second stage inclusions homogenize completely at temperatures of 219–317 °C and have salinities of 1.56–11.12 wt% NaCl equivalent, while third stage inclusions homogenize completely at temperatures of 195–319 °C and have salinities of 2.73–13.33 wt% NaCl equivalent. In contrast, quartz grains that formed during the last mineralization stage contain mainly FIA3-type inclusions that yield homogenization temperatures of 126–233 °C and salinities of 0.48–6.72 wt% NaCl equivalent. The microthermometric data indicate that the ore-forming system evolved from a CO 2 -rich mesothermal fluid into a CO 2 -poor fluid. The existence and microthermometric characteristics of AC-, PC-, and A-type inclusion assemblages (FIA2) within a single thin section of grains that formed during the second and third stages show that ore fluids underwent unmixing during the syn -ore mineralization stages, due to pressure and temperature fluctuations. The microstructural deformation of auriferous samples indicates that both ductile and brittle deformation occurred during the syn -ore mineralization. Based on the inference that fluids were immiscible in FIA2, trapping pressures during ore formation are estimated at 127–276 MPa. Assuming a fluid pressure regime controlled by fault-valve activity, these pressures are equivalent to a mineralization depth of 9.2–14.0 km. The depth to which erosion occurred in the study area has been calculated as ~10.3 km since the formation of the deposit at 130 Ma, which suggests good prospecting potential for gold at depth in Dayingezhuang. Unlabelled Image • Three types of FIA were identified in the Dayingezhuang deposit. • Large scale fluid immiscibility did take place in syn -ore stages. • Metallogenic depth vs. erosion depth can be used for prospecting potential. • The space with deep gold exploration is expectable at Dayingezhuang gold. [ABSTRACT FROM AUTHOR]
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Description
Abstract:The Dayingezhuang deposit is a representative large gold deposit within the Zhao-Ping fault zone in Jiaodong Peninsula, eastern China, and contains gold reserves of 170 t with an average grade of 3.10 g/t. The orebodies are hosted in the Late Jurassic Linglong granite intrusion and are Jiaojia-type (disseminated- or stockwork-style) ores. Mineralization and alteration are structurally controlled by the NE- to NNE-striking Linglong detachment fault located near the central section of the regional Zhao-Ping fault zone. Mineralization can be divided into primary and supergene periods. The primary period can be further divided into four hydrothermal stages: I) pyrite–(K-feldspar)–sericite–quartz; II) auriferous quartz–pyrite; III) quartz–gold–polymetallic sulfides; and IV) quartz–carbonate. Gold was mainly deposited in the second and third stages. Three types of fluid inclusion were observed (in decreasing order of abundance): AC-type (aqueous–carbonic), A-type (aqueous), and PC-type (pure carbonic). Based on petrographic, microthermometric, and laser Raman spectroscopic analyses of these fluid inclusions, three types of fluid inclusion assemblage (FIA) were identified in the quartz grains: FIA1 (AC- and PC-type), FIA2 (AC-, PC- and A-type), and FIA3 (A-type). First stage quartz grains contain mainly FIA1-type inclusions, with trapping temperatures of 305–388 °C and salinities of 4.28–8.51 wt% NaCl equivalent. Quartz grains that formed in the second and third mineralization stages contain all three types of FIA. Second stage inclusions homogenize completely at temperatures of 219–317 °C and have salinities of 1.56–11.12 wt% NaCl equivalent, while third stage inclusions homogenize completely at temperatures of 195–319 °C and have salinities of 2.73–13.33 wt% NaCl equivalent. In contrast, quartz grains that formed during the last mineralization stage contain mainly FIA3-type inclusions that yield homogenization temperatures of 126–233 °C and salinities of 0.48–6.72 wt% NaCl equivalent. The microthermometric data indicate that the ore-forming system evolved from a CO 2 -rich mesothermal fluid into a CO 2 -poor fluid. The existence and microthermometric characteristics of AC-, PC-, and A-type inclusion assemblages (FIA2) within a single thin section of grains that formed during the second and third stages show that ore fluids underwent unmixing during the syn -ore mineralization stages, due to pressure and temperature fluctuations. The microstructural deformation of auriferous samples indicates that both ductile and brittle deformation occurred during the syn -ore mineralization. Based on the inference that fluids were immiscible in FIA2, trapping pressures during ore formation are estimated at 127–276 MPa. Assuming a fluid pressure regime controlled by fault-valve activity, these pressures are equivalent to a mineralization depth of 9.2–14.0 km. The depth to which erosion occurred in the study area has been calculated as ~10.3 km since the formation of the deposit at 130 Ma, which suggests good prospecting potential for gold at depth in Dayingezhuang. Unlabelled Image • Three types of FIA were identified in the Dayingezhuang deposit. • Large scale fluid immiscibility did take place in syn -ore stages. • Metallogenic depth vs. erosion depth can be used for prospecting potential. • The space with deep gold exploration is expectable at Dayingezhuang gold. [ABSTRACT FROM AUTHOR]
ISSN:03756742
DOI:10.1016/j.gexplo.2019.06.001