DISTRIBUTION AND STYLES OF HYPOGENE ALTERATION IN THE MIAMI-INSPIRATION PORPHYRY CU(-MO) DEPOSIT, GLOBE-MIAMI DISTRICT, ARIZONA

The Miami-Inspiration porphyry Cu(-Mo) deposit, Globe-Miami district, Arizona, is a Laramide porphyry system that has been a locus of substantial copper production and mining innovation in the Copper State since the late 19th Century. The purpose of this study is to broaden the present understanding of hypogene alteration and zoning within the deposit. The Miami-Inspiration deposit is genetically associated with the 67-61 Ma Schultze Granite, which intruded the ~1.7 Ga Pinal Schist in the form of several chemically similar, yet texturally heterogeneous, stocks and dikes. Multiple generations of generally NE- and SW-dipping mid-Tertiary normal faults have dismembered the deposit, with originally shallower features exposed towards the northeast, revealing ~3-10km paleodepth. Pre-extension structures, such as the Sleeping Beauty fault to the north of the deposit, may have also influenced ore distribution and post-Laramide stress regimes.

In this study, we use bench-scale mapping and core logging to document the character of hypogene alteration and mineralization in the deposit’s potassic- and sericitic-altered zones. Further, we document deeper forms of alteration exposed in the southwestern area of the deposit including coarse muscovite (“greisen”) and early dark micaceous (EDM) veins. At least two generations of quartz+K-feldspar±biotite veins are present. In one locality, EDM veins are spatially associated with an earlier generation of quartz+K-feldspar±biotite veins. In some bench faces in the potassic and transitional potassic-sericitic zones, quartz+K-feldspar±biotite veins are offset by quartz+molybdenite±pyrite veins. Quartz+pyrite±sericite veins overprint potassic assemblages in the sericitic zone, while coarse muscovite overprints sulfide-poor potassic veins in deeper exposures in southwestern portions of the system. Propylitic alteration, in the form of chlorite+epidote+pyrite+calcite±magnetite±albite, is observed on the northern fringes of the deposit. Given that ~60% of the Globe-Miami district is covered by younger sedimentary and volcanic rocks, an improved understanding of the hypogene alteration zoning at Miami-Inspiration will have implications for district-scale and regional mineral exploration.