|Other Titles||Fluid Inclusion constraints on the origin of Zhifang Mo deposit Songxian county, Henan provine|
|Keywords||纸房钼矿床 矿床地质 流体包裹体 造山型钼矿 秦岭造山带|
Zhifang Mo deposit
Orogenic Mo deposit
The Zhifang Mo deposit in Songxian County, Henan Province is located in the Xiong'er Terrane in northern Qinling orogen. Its orebodies, occurring as quartz-veins, are hosted in volcanic rocks of the Xiong' er Group and controlled by subsidiary faults of the Machaying fault which is the south boundary fault of the Xiong' er terrane. Three stages of hydrothermal ore-forming process are recognized, Early, Middle and Late, characterized by quartz-pyrite, quartz-sulfides and carbonates, respectively. The early-stage quartz-veins or mineral assemblages are structurally deformed and brecciated. Three types of fluid inclusions, i.e. CO(2)-H(2)O, H(2)O-NaCl and daughter mineral-bearing, are observed in quartz-crystals formed in early and middle stages; while the late-stage calcites only contain H(2)O-NaCl inclusions. From early to late stages, homogeneous temperatures of fluid inclusions decrease from 467 similar to 380 degrees C (E), through 360 similar to 250 degrees C (M), to 240 similar to 137 degrees C (L); salinities change from 0.18% similar to 13.13% NaCl. eqv (E), through 0.01% similar to 20.70% NaCl. eqv (M), to 0.35% similar to 12.85% NaCl. eqv (L). Salinities of the daughter crystal-bearing fluid inclusions which only occur in early and middle stages range from 28.04 to 31.35% NaCl. eqv. The early-stage daughter crystal-bearing fluid inclusions were captured from undersaturated solution, and those of middle-stage were captured from both oversaturated and undersaturated solutions. Homogeneous pressures of fluid inclusions of the early and middle stages cluster into two groups of 180 similar to 220 MPa and 40 similar to 80 MPa, respectively, implying that fluid-systems alternated between hydrostatic and lithostatic at the depth of 6km similar to 8km. Homogeneous pressures of late-stage fluid inclusions range 50 similar to 80 MPa, suggesting an open-space filling hydrostatic fluid-system. The alternating hydrostatic-lithostatic fluid-systems, analogous to the fault-valve model established for orogenie-type gold deposits, resulted from oscillating fluid-boiling and/or coseismic broken and healing. Boiling-related escape of volatile such as CO(2) made the fluids condensed or oversaturated and elevated the fluids' pH value and reducibility, resulting rapid precipitation of ore-forming materials such as MoS(2). Therefore, the Zhifang Mo deposit can be genetically assigned to be orogenic-type ore-system formed during intercontinental collision regime. Considering that most fluid inclusions within quartz crystals formed in the early and middle stages are homogenized into gas-phase, the space beneath the current prospecting level is potential for high-grade Mo-ores.
|Appears in Collections:||造山带与地壳演化教育部重点实验室|