Fluid Inclusions In Stage Research Articles

Mineralogy and fluid inclusion study of the southern Amethyst vein system, Creede mining district, Colorado

Ag mineralization occurs as vein fillings and disseminations confined to areas of high fracture density and brecciation in the hanging wall of the Amethyst fault and vein. Paragenesis is divided into two main stages: 1 is a sulfide-poor assemblage characterized by rhodochrosite, quartz, barite, and an absence of silver; 2 represents a complex event made up of three substages. Disseminated mineralization in the study area appears to be related to stage 2. Analysis of fluid inclusions in stage 2 vein quartz showed that average homogenization temperatures and salinities decrease in a regular manner from lower to upper levels of the mine. Inclusions in stage 2 quartz from the lower mine levels had an average T h = 238 degrees C and an average salinity of 9.8 equivalent weight percent NaCl. Those in the uppermost level had an average T h = 170 degrees C and an average salinity of 6.5 equivalent weight percent NaCl. The rapid drop in temperature and dilution of hydrothermal solutions which was a result of mixing with near-surface waters caused the deposition of the high-grade Ag ores in the southern Amethyst vein system.--Modified journal abstract.

Ore fluids in the porphyry copper deposit at Copper Canyon, Nevada

The large, low-grade copper and gold deposit at Copper Canyon, Lander County, Xevada, formed in the contact metasomatic environment adjacent to a shallow Tertiary intrusion. Vein and disseminated chalcopyrite-pyrite-pyrrhotite-arsenopyrite mineralization, with lesser amounts of gold, galena, sphalerite, marcasite, and siderite occur in the Upper Cambrian Harmony and Middle Pennsylvanian Battle Formations. Studies of fluid inclusions in stages of vein quartz and in healed fractures through quartz phenocrysts and pebbles reveal the presence of very saline, sometimes CO 2 -rich fluids in the early and middle stages of mineralization. Ore fluid salinities during the base metal mineralization were approximately 40 wt percent, and temperatures were near 375 degrees C. Circulation of this hot brine was apparently restricted to an elongate highly fractured zone within 3,000 feet laterally of the intrusive. Later fluids in this central zone were somewhat cooler, near 300 degrees C, and had significantly lower salinities in the range 12 to 1.2 wt percent. Smaller lode deposits approximately 1 to 5 miles from the intrusion appear to have formed from low to moderate salinity fluids at temperatures generally in the range 250 to 335 degrees C. Geologic and fluid considerations suggest formation at approximately 6,000 feet in depth.