Rampart Copper

Occurrence, Inactive

Commodities and mineralogy

Main commodities Cu
Ore minerals chalcopyrite; malachite; pyrite

Geographic location

Quadrangle map, 1:250,000-scale LG
Quadrangle map, 1:63,360-scale C-5
Latitude 65.6647
Longitude -149.0513
Nearby scientific data Find additional scientific data near this location
Location and accuracy The copper occurrences were exposed during excavation for the Trans-Alaska Pipeline and are situated on the right-of-way located in SE¼NE¼, SE¼SE¼, and NW¼SE¼ Section 29, T. 10 N., R. 7 W., Fairbanks Meridian. The site is along the pipeline service pad on the north-facing hillslope to the Hess Creek valley.

Geologic setting

Geologic description

The Rampart Group is mapped by Weber, and others (1992) as Triassic and Permian extrusive and intrusive mafic rocks with some undifferentiated sedimentary rocks. Brosge and others (1969) noted that diabase dikes and larger bodies of gabbro and augite diorite are common within the mapped boundaries of the Rampart Group’. A dike of hornblende diorite in the Rampart Group south of Hess Creek in the Livengood Quadrangle was found to locally contain as much as 10 percent sulfide.
Geologic map unit (, )
Mineral deposit model Porphyry copper (Cox and Singer, 1986; model 17).
Mineral deposit model number 17
Age of mineralization Host rock diorite is Permian; age of mineralization is unknown.
Alteration of deposit No significant alteration.

Production and reserves

Workings or exploration
In the 1970s the Bureau of Mines made mineral evaluation studies of the Trans-Alaska Pipeline Corridor for the Bureau of Land Management. A dike of hornblende diorite south of Hess Creek in the Livengood Quadrangle was found to locally contain as much as 10 percent sulfide. Copper minerals occur in chert and diorite float at several sites locally; the best assay value was 1.56 percent copper in a select hand sample. Further examination found copper mineralization to be limited and discontinuous, and associated with diorite dikes and sills. Copper minerals were seen in hand specimen. A few blebs of chalcopyrite were noted in the diorite (?) and malachite coated fractures in the chert over a small area near one of the diorite (?) dikes and meta-siltstone. Investigation included several ground magnetic surveys, soil sampling, and general reconnaissance of the area (McDermott and others, 1981). Analytical results for soil and rock samples are reported in Averett and Barker, 1981.
Due to the low concentrations and low tonnages implied by a dike or sill-like occurrence of disseminated copper in diorite, and the lack of significant copper mineralization, alteration, mineral zoning and alteration zoning typical of copper-porphyry deposits, no further work was recommended.
Indication of production None

Additional comments

Access to the pipeline pad requires a temporary use permit from Alyeska Pipeline Service Co. Splits of most samples collected by the U.S. Bureau of Mines and referenced in this report have been archived at the Alaska Geologic Materials Center, Anchorage, Alaska and are available for review.

References

Reporters J.C. Barker
Last report date 3/15/2016