15:30 〜 15:45
[HRE12-06] Mineral and fluid chemistry variations in high-sulfidation epithermal systems: Constraints from cathodoluminescence and chemistry of quartz and fluid inclusions
キーワード：fluid inclusions, mineral chemistry, LA-ICPMS, quartz, high-sulfidation epithermal
The ubiquity of quartz in hydrothermal systems makes it a good candidate for developing potential vectoring tools for precious and base-metal mineralization. Cathodoluminescence and trace element geochemistry have been used to differentiate quartz related to porphyry, orogenic and epithermal systems. However, most of the studies and compilations about trace element signatures and fluid chemistry in epithermal quartz are based on samples from low- and intermediate-sulfidation epithermal deposits, while data from high-sulfidation epithermal systems are scarce. In this study, we focus on quartz and quartz-hosted fluid inclusions which are closely related to enargite-gold mineralization to document the characteristics associated with high-sulfidation epithermal systems. Samples were taken from the Northwest ore body in Lepanto, Mankayan, Philippines. The Northwest orebody is characterized by an early stage of quartz-pyrite-gold veins and a later stage of enargite-quartz veins. Most of the mineralization is hosted by the metavolcanic basement and dacitic pyroclastic rocks, which have been altered to quartz, kaolinite and alunite.
Vein quartz intergrown with enargite has comb and zonal textures, indicating symmetrical growth from the wall rock towards the center of the vein. The earliest quartz crystals show dark blue luminescence with minor violet zones in optical-CL , followed by growth of zonal quartz with distinct white luminescence, then overgrown by clear comb quartz with light violet luminescence.
A younger quartz vein cutting the enargite-quartz vein exhibits cockade, zonal, and comb textures with green luminescence. The boundary between the older blue-luminescent quartz and the green-luminescent quartz is characterized by a feathery recrystallization texture with white luminescence.
The early blue-luminescent quartz contains an average of 700 ppm Al and 9 ppm Ti, while the later light-violet-luminescent quartz contains an average of 80 ppm Al and 1 ppm Ti. The youngest green-luminescent quartz contains the lowest amount of Al and Ti with an average of 20 ppm and 0.8 ppm, respectively. Profile analysis of the Ti content in quartz from the periphery to the center of the vein also shows progressive decrease, indicative of a cooling trend. The white-luminescent and green-luminescent quartz show significantly higher As (7-24 ppm) and Sb (60-200 ppm) contents, than the earlier formed quartz.
Liquid-rich aqueous fluid inclusions in the early blue-luminescent quartz have slightly higher salinity (5 wt% NaCl eq.) than that of the later light-violet luminescent quartz (average 4 wt%). Potassium and Rb concentrations of the fluid inclusions in the early blue-luminescent quartz range 1000-2000 ppm and 10 to 85 ppm, respectively. Those hosted in the light-violet-luminescent quartz contain slightly lower K at 100-1000 ppm and Rb at 1 to 37 ppm. The concentrations of Sb, As and Cu in the fluid inclusions of the early and late quartz overlap with each other and have average values of 60 ppm, 176 ppm and 230 ppm, respectively. The As content measured from epithermal quartz-hosted fluid inclusions of the Northwest orebody is within the range of that reported from vapor-rich fluid inclusions in porphyry-type quartz of other deposits, but lower when compared to that of the liquid-rich fluid inclusions in porphyry-type quartz (Klemm et al., 2007). Copper content in the fluid inclusions of the Northwest ore body epithermal quartz is slightly higher than the liquid-rich fluid inclusions, but significantly lower than that of the hypersaline multiphase fluid inclusions in porphyry-type quartz (Klemm et al., 2007).
Vein quartz intergrown with enargite has comb and zonal textures, indicating symmetrical growth from the wall rock towards the center of the vein. The earliest quartz crystals show dark blue luminescence with minor violet zones in optical-CL , followed by growth of zonal quartz with distinct white luminescence, then overgrown by clear comb quartz with light violet luminescence.
A younger quartz vein cutting the enargite-quartz vein exhibits cockade, zonal, and comb textures with green luminescence. The boundary between the older blue-luminescent quartz and the green-luminescent quartz is characterized by a feathery recrystallization texture with white luminescence.
The early blue-luminescent quartz contains an average of 700 ppm Al and 9 ppm Ti, while the later light-violet-luminescent quartz contains an average of 80 ppm Al and 1 ppm Ti. The youngest green-luminescent quartz contains the lowest amount of Al and Ti with an average of 20 ppm and 0.8 ppm, respectively. Profile analysis of the Ti content in quartz from the periphery to the center of the vein also shows progressive decrease, indicative of a cooling trend. The white-luminescent and green-luminescent quartz show significantly higher As (7-24 ppm) and Sb (60-200 ppm) contents, than the earlier formed quartz.
Liquid-rich aqueous fluid inclusions in the early blue-luminescent quartz have slightly higher salinity (5 wt% NaCl eq.) than that of the later light-violet luminescent quartz (average 4 wt%). Potassium and Rb concentrations of the fluid inclusions in the early blue-luminescent quartz range 1000-2000 ppm and 10 to 85 ppm, respectively. Those hosted in the light-violet-luminescent quartz contain slightly lower K at 100-1000 ppm and Rb at 1 to 37 ppm. The concentrations of Sb, As and Cu in the fluid inclusions of the early and late quartz overlap with each other and have average values of 60 ppm, 176 ppm and 230 ppm, respectively. The As content measured from epithermal quartz-hosted fluid inclusions of the Northwest orebody is within the range of that reported from vapor-rich fluid inclusions in porphyry-type quartz of other deposits, but lower when compared to that of the liquid-rich fluid inclusions in porphyry-type quartz (Klemm et al., 2007). Copper content in the fluid inclusions of the Northwest ore body epithermal quartz is slightly higher than the liquid-rich fluid inclusions, but significantly lower than that of the hypersaline multiphase fluid inclusions in porphyry-type quartz (Klemm et al., 2007).