ANALYZING COPPER MINERALIZATION WITHIN THE HYDROTHERMAL ALTERATION AND MINERAL ASSEMBLAGES WITHIN QUARTZ MONZONITE PORPHYRY SAMPLES AT THE ANN MASON PORPHYRY DEPOSIT, LYON COUNTY, NEVADA

The Ann Mason porphyry deposit is located at the western side of the Basin and Range province, West of Yerington in Lyon County, Nevada. The Ann Mason is a copper porphyry deposit with trace amounts of gold, silver, and molybdenum. The Cu mineralization is commonly hosted within the quartz monzonite porphyry, the granite porphyry dikes, and also the overlying lithologies of the Yerington batholith. The Cu within the Ann Mason exists as sulfides deposited by magmatic-hydrothermal fluids likely released from the dikes; these hydrothermal fluids are likely also the cause for hydrothermal alteration within the overlying rocks in the area. It is noted that potassic, propylitic, sodic-calcic, sericitic and advanced argillic alteration types exist within the Ann Mason and hydrothermal fluid sources vary within the deposit, but potassic alteration occurs along the porphyry dike swarm and occurs primarily with Cu mineralization. The purpose of this project is to characterize the occurrence of Cu minerals in terms of their associated alteration and ore mineral assemblages. Using transmitted and reflected light microscopy I am analyzing samples of the quartz monzonite porphyry from various drill cores. A fellow researcher is conducting a similar analysis on samples of granodiorite and porphyritic quartz monzonite within the Ann Mason. As a result we are able to assess the effects of rock type on the mineralization and alteration. From preliminary data, I have observed Cu existing as bornite and chalcopyrite, with chalcopyrite appearing as inclusions within the bornite. Dominant minerals seen during the preliminary work are quartz and potassium feldspar along with sagenitic biotite in some samples and possible muscovite in other samples. The occurrence of potassium feldspar and sagenitic biotite together suggests a dominant potassic alteration in some of the quartz monzonite porphyry samples. Determining more about how the Cu mineralization at Ann Mason relates to the alteration and mineral assemblages within the region will expand our understanding about porphyry deposits and similar Cu deposit types. This will also expand our knowledge about the source for alteration and their respected Cu percentages, which will provide more insight about how Cu deposits form and assist in locating future deposits.