THE SUNNYSIDE-TAYLOR-HARDSHELL SYSTEM: EXPLORATION IMPLICATIONS OF A REMARKABLY COMPLETE PORPHYRY COPPER-SKARN-CARBONATE REPLACEMENT MINERALIZATION SPECTRUM IN SOUTHERN ARIZONA

The well-delimited, but weakly mineralized Sunnyside Porphyry Copper system was emplaced into a typical southeastern Arizona section of Paleozoic carbonates and nonreactive clastic units. These were complexly thrust-faulted in the Nevadan orogeny and subsequently eroded prior to being covered by Jurassic intermediate volcanic rocks. The Sunnyside porphyry was intruded in the late Laramide with exceptionally voluminous zoned skarn and carbonate replacement mineralization deposited coevally in the surrounding Paleozoic sedimentary rocks. The overall system shows a complete spectrum of ore types from Porphyry Copper mineralization, through proximal Cu-rich skarn, through Zn-Pb and Pb-Zn massive sulfide replacements, to distal primary (?) oxide Ag-Mn mineralization. Mineralization in the overlying Jurassic volcanic units consists of sulfide veins and well-developed metalliferous silicification.

The Taylor Manto is an enormous (>150 million tons) high-grade, tabular Cu-Zn-Pb-Ag sulfide-mineralized body that has been traced down-dip to roughly 1200m depth. It occurs in the uppermost part of the Paleozoic sequence approximately 1000m above the lower Paleozoic Escabrosa-Martin-Abrigo formations that host important the replacement mineralization at Bisbee, Morenci, and Magma. A significantly altered, nearly vertical, NW-striking outcrop of these units crops out less than 2 km south of the Taylor Manto, indicating that this potentially more productive host rock sequence may lie at shallow depths beneath Jurassic rocks elsewhere in the camp. Comparison with other copper porphyry-related skarn-replacement systems suggests that additional mineralized corridors may exist around the Sunnyside center and be explored by tracing mineralization in the Jurassic volcanics to depth into the underlying sedimentary rocks.

Perhaps the most important aspect of Sunnyside is the recognition that disproportionately large volumes of skarn and replacement mineralization can surround a relatively weak Porphyry Copper system. Recent 1:6000 scale mapping, geochemical sampling and NSAMT geophysics have identified multiple, skarn-CRD targets located around the margins of the Sunnyside porphyry complex and on-going work is focused on targeting mineralization located around additional porphyry centers.