Isle Royal Mine, Isle Royal Mine group, Helvetia, Helvetia-Rosemont Mining District, Pima County, Arizona, USAi

Regional Level Types
Isle Royal Mine	Mine
Isle Royal Mine group	- not defined -
Helvetia	Town (Former)
Helvetia-Rosemont Mining District	Mining District
Pima County	County
Arizona	State
USA	Country

A former small surface and underground Cu-Ag-Au-Mo-W mine located in the SE¼NW¼ sec. 24, T18S, R15E, 1¼ miles east of Helvetia and 1,000 feet south of the Copper World Mine, and 28 miles SE of Tucson. It is near the axis of the range, in the north slope of the spur of Monument Mountain. Discovered by C.E. Hughes in the early 1880's (1882 ?). Development work commenced in 1904. Closed 1905. Reopened about 1908 and worked until ore became too lean. The Isle Royal Mine underlies the Copper Fend, Copper World and the Owosko patented claims, all of which are part of the Helvetia property owned by ASARCO (1992).

Mineralization is a pipe-like ore body hosted in Escabrosa Limestone, Horquilla Limestone; Abrigo Formation; and, Bolsa Quartzite. Located on a contact between Paleozoic limestone and Mesozoic granite, near a fault. An associated rock unit is the Continental Granodiorite. The contact dips 68ºN. The alaskite aplite dike of the Copper World Mine lies nearby on the east and probably exerted a favorable influence on the ore deposition, as may have also the stock of granite porphyry not far distant. Ore control was altered limestone along the fault. Alteration was oxidation down to the 330 foot level; also, pyrite-chalcopyrite-gossan and skarn. Malachite and azurite found in supergene zone, secondary after pyrite and chalcopyrite.

The oxidized zone extends from the surface to the 330 foot level. The ore here includes a large chimney-like body extending from the 100 foot to the 300 foot levels. This ore is all copper carbonates (malachite and azurite), and is contained in relatively firm limestone.

Good copper sulfide ore, consisting principally of cupriferous pyrite and chalcopyrite, was encountered in moderate-sized bodies on the 400 level and continued down to the 600 level, below which it reported pinched out.

Local structures include a NW-striking thrust and normal faulting, homoclinal. Regional trends include tilting and broad open folds in the south and extensive faulting in the north.

Workings include an old shaft sunk to the first level in 1904. An 800-foot, double-compartment vertical main shaft and about 4,000 feet of work on 7 levels were subsequently developed. Deepest mine in the area at 243.84 meters. Workings underlie the Little Dave.

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Link to USGS MRDS:	10039411

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References