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The AAPG/Datapages Combined Publications Database

Utah Geological Association


Geology and Geologic Resources and Issues of Western Utah, 2009
Pages 143-156

Geology and Exploration at the Crypto Zinc-Indium-Copper-Molybdenum Skarn Deposit, Fish Springs Mining District, Juab County, Utah

C.F. Staargaard


The Crypto deposit is a zinc-rich skarn situated in the northeastern part of the Basin and Range province in Utah, approximately 160 kilometers southwest of Salt Lake City. Coarse-grained sphalerite and minor chalcopyrite are associated with magnesioferrite/magnetite-rich magnesian skarn in a sequence of Cambrian to Ordovician carbonates where they have been cut by a high-level quartz monzonite intrusive of late Eocene age (dated at 38.5 ┬▒ 1.0 Ma). Mineralization tends to be developed in more shaly or silty members in the sequence and is generally oxidized to a depth of about 250 meters, sphalerite having been converted to zincite, smithsonite, hemimorphite, and hydrozincite.

Molybdenite is commonly found along fractures, in quartz-molybdenite-pyrite veinlets in the intrusive rocks, and also as disseminations in the adjacent skarn. The general distribution of mineralization on the Crypto property shows indications of porphyry-style zoning with a lower Mo-bearing zone grading upwards and outwards through Cu, Zn, and then Pb and Ag-rich zones with increasing distance from the intrusive.

In 1993, Cyprus Minerals estimated a historical resource of 5.44 million tonnes grading 8.7% zinc in two lower sulfide zones and a further 2.8 million tonnes grading 7.0% zinc in a near-zsurface oxide zone. Lithic Resources purchased the property in 2005 and from 2006 to 2008, completed various exploration programs including 10,639 meters of core drilling aimed largely at confirming and expanding the historical zinc resource. Numerous high-grade intercepts of zinc ┬▒copper mineralization were returned as well as several significant intervals of molybdenum mineralization in both skarn and as porphyry-style quartz-pyrite veinlets in intrusive rocks. A particularly interesting development has been the discovery of unusually high levels of indium associated with the zinc mineralization.

An updated estimate of the zinc-copper-indium resource is in preparation and preliminary metallurgical test work on both oxide and sulfide mineralization is scheduled. Follow-up work under consideration includes drilling to continue confirming and expanding both sulfide and oxide zinc-copper-indium mineralization, more detailed metallurgical test work, exploration drilling to test for outlying Zn skarn and replacement Ag mineralization, as well as deep drilling to test for the possibility of a major, underlying porphyry molybdenum system.

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