Project Summary
Historical reports indicate large tonnage capacity with oxidized zones 6 to 30 feet wide averaging 3% copper, with silver credits. Massive magnetite bodies up to 100 feet thick were reported to carry 1.5% copper disseminated throughout. Previous production from the Tempest claim included carload shipments of hand-sorted ore returning 8% to 10% copper. Shallow surface openings have exposed bornite mineralization averaging 5% copper. The deposit type is described as practically identical to the profitable Empire Copper property at Mackay.
The Sims Copper project is located in Lemhi County, Idaho, near the summit of the Lemhi Range, approximately 6 to 8 miles southwest of the historical Gilmore lead-silver mines. Access is available from the Birch Creek Valley.
Geology
The project targets multiple lens-shaped bodies of massive magnetite and disseminated copper mineralization located along the contact of quartz diorite and marble (limestone). The mineralized zones vary significantly in size, with reports of bodies up to 100 feet thick occurring along the intrusive margins.
Metals contained within the deposits include copper, gold, silver, and iron. The copper mineralization is generally irregular and traverses the magnetite veins. Ore minerals identifiable in hand specimen include fine-grained bornite, copper carbonates, and "liver-colored" copper oxides. Alteration minerals associated with the ore include garnet, epidote, serpentine, and amphibole.
In addition to the massive magnetite bodies, the property exhibits broad zones of garnet rock containing soft brown iron and copper oxides. Specific deposits mapped on the property include the "Hematite," "Divide," and "Old Timer" zones, which show magnetite replacement along fractures in the limestone.
History
Located directly in the strike of the Gilmore fissure system, the property was developed through a series of surface cuts, pits, and shallow underground workings. Significant historical activity focused on the Tempest claim, where a broad zone of mineralization yielded shipments of 8% to 10% copper with historical gold values of approximately $10.00 per ton.
State Inspector of Mines reports described the area as a body of eruptive granite 4,000 feet long and 2,000 feet broad, bordered by quartzite and limestone. Early development identified interesting outcrops including a body of massive magnetite ore three to six feet thick with a uniform dissemination of bornite averaging 5% copper.
In 1961, the property was held by Howard Sims, who bulldozed a jeep road for access and facilitated geological mapping. This work confirmed the presence of magnetite and limonite veins, including a hematite deposit on the ridge summit exposed for 50 feet along strike. The historical reports emphasize the "permanency and importance" of the surface deposits and the potential for high-grade copper minerals.
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| Zone / occurrence | Width / thickness | Reported grade |
|---|---|---|
| Oxidized zones | 6 to 30 ft wide | 3% copper average, with silver credits |
| Massive magnetite bodies | Up to 100 ft thick | 1.5% copper disseminated throughout |
| Tempest claim shipments (hand-sorted carloads) | — | 8% to 10% copper; gold values of approx. $10.00 per ton |
| Bornite-bearing magnetite outcrop | 3 to 6 ft thick | 5% copper average in shallow surface openings |