New Mexico Geological Society Annual Spring Meeting — Abstracts

The Jones Hill massive sulfide deposit is located in the Sante Fe mining district on the border ofSante Fe and San Miguel counties approximately 15 miles northeast of Sante Fe. The area is part ofthe Proterozoic Pecos greenstone belt in the southern Sangre de Cristo Mountains. The Jones Hill mine was worked in the 1930's by three adits and one shaft but no production data exists from that period. The massive sulfide deposit at the Pecos mine 4 miles to the east produced over 2 million tons ofore with average grades of 12.95% zinc, 4.00% lead, .078% copper, 3.4 ppm silver, and .011 ppm gold before shutting down in 1939 due to bad ground at depth.

The massive sulfide deposits are hosted by Proterozoic volcanic sequences of bimodal mafic-felsic composition. The deposits are generally lensoid and stratabound within a host of metavolcanic and metaclastic rocks. Deposition is from high temperature hydrothermal solutions associated with volcanism. The deposits are typically mined for lead and zinc with precious metals as a byproduct. The Jones Hill deposit is a Proterozoic volcanogenic polymetalic deposit with copper-Iead-zinc-silver-gold ore reserves projected to be 12 million tons in two blocks; an up faulted block projected at 5 million tons and a lower block of7 million tons ofore. Upper block ore grades average 4.60% zinc, 2.47% copper, and 0.072 ppm gold, the lower block ore grades average 3.81% zinc, and 4.44% copper with an increase in the down dip direction.

The massive sulfide deposit occurs at the contact between Proterozoic rhyolite domes and overlying metamorphic rocks. The volcanic package was intruded by granite, mineralized, and folded and faulted. There is an angular unconformity between the Proterozoic volcanics and the overlying Paleozoic sediments. The Jones Hill thrust fault then offset the deposit 2,000 feet. The primary ore minerals are sphalerite, galena, and chalcopyrite. Bomite, argentite, molybdenite, proustite, native gold, and tetrahedrite are found in lesser amounts. The sulfide minerals in the gangue material include pyrite, arsenopyrite, and pyrrhotite. The gangue minerals are extensive but basically contain mafic minerals along with quartz, flourite. kaolinite, sericite, talc, and calcite. Alteration is stronger in the footwall near the ore zone.