The Helen Zone is located just northwest of the Cove open-pit Gold mine which is located 35 miles southwest of Battle Mountain in Lander County, Nevada. The Helen Zone consists of horizontal, bedding-replaced, disseminated, Carlin-style mineralization that is hosted in decarbonatized and decalcified carbonate lithologies. Economic mineralization of the Helen Zone is attributed to fluids bearing precious metals associated with two magmatic pulses that formed igneous intrusions ~41.5 and ~39 Ma. The Helen Zone is structurally controlled by steeply dipping thrust and normal faults which aid later hydrothermal fluids coming off igneous intrusions to become mobilized and emplaced in decarbonatized Home Station (TRas) dolostone and decalcified Favret (TRfv) limestone. Previous studies of the Helen Zone characterized these igneous intrusions in addition to mineralization that takes place in carbonate lithologies.
This study consisted of twenty samples that were obtained from eight of Premier Gold Mines Limited’s exploratory drill holes from the Helen Zone. Samples were analyzed using transmitted and reflected light microscopy in addition to energy dispersive X-ray analysis (EDAX) for the identification of mineral and vein-types that retain precious metals. Carbonate, sulfide, and silicate vein phases were identified and analyzed for their concentrations in weight percentages of gold (Au), silver (Ag), platinum (Pt), arsenic (As), and other accessory elements in order to characterize the chemistry of the vein minerals. The EDAX analyses yielded results that showed carbonate veins contain highest grades of Ag, sulfide veins contain highest grades of Au and Pt, and silicate veins contain lowest grades of Au, Ag, Pt, and As. Economic mineralization at the Helen Zone can be attributed to hydrothermal bisulfide fluid complexes that had the capability to mobilize and precipitate precious metals in carbonate host rocks that we see today. Paragenesis of veining at the Helen Zone was determined as having multiple episodic events that took place, based on analyzing carbonate and sulfide vein-types. Relative dating of vein-types suggests that sulfide veins are older than carbonate veins which in turn are older than silicate veins.