MAGMATIC AFFILIATIONS FOR ENIGMATIC GOLD DEPOSITS IN THE NORTHERN BATTLE MOUNTAIN MINING DISTRICT, NEVADA

Interest in the +10 M oz Au Battle Mountain (BM) district has shifted from early focus on porphyry and skarn Cu deposits in its south part to Au skarn and distal-disseminated Au deposits mostly in the north part. At Lone Tree (LT), Au is present mainly in Ord Valmy Formation (Ov) and Penn-Perm Antler sequence (PIPa), as well as in Miss-Perm Havallah sequence (PMh) and an altered 38ÐMa dike. Buffalo Valley and North Peak were developed primarily in PMh rocksÑintrusive rocks are present at both. Most ore at Trenton Canyon formed in Ov, with less in PIPa; sericitically altered dikes are 35 Ma. The 41ÐMa 2 M oz Redline Au skarn resource, hosted in PMh, occurs between LT and North Peak. Deeply oxidized Au deposits at Marigold are present mostly in Ov; overlying PIPa also hosts ore. Exploration focus at Marigold initially was on PIPa, but Ov now hosts a dominant proportion of both reserves and produced oz Au. Recent work has added >1 M oz Au to reserves, hosted by Ov and PIPa, as well as a mineralized presumably Tert dike. This is the first occurrence of an igneous rock actually being ore grade at Marigold, which historically has been distinguished by lack of igneous rock. Despite near absence of igneous rock in Au deposits in the north part of BM, isotopic studies of select samples from Au deposits suggest magmatic waters in their origin. Sulfur isotopic ratios, mostly from hydrothermal barite at the 8 South deposit, cluster near +10 per mil, suggesting derivation of S primarily from a homogeneous source, probably magma. Isotopic ratios of fluid-inclusion waters in barite from LT cluster on a mixing line between magmatic and middle Tertiary meteoric water. Isotopic ratios, as well as high T, highly saline fluid inclusions in mineralized veins at LT, and sericitically altered dikes associated with AuÐmineralized rocks, thus are all compatible with close magmatic affiliations for genesis of these Au deposits.