RIASSUNTO
Abstract
During, the late summer of 1971, marine geologists and geophysicists of the University of Wisconsin Sea Grant Minerals Program conducted a combined seismic, magnetometry, and dredging survey in Lake Superior waters surrounding the outer Keweenaw Peninsula. The principal objective of this continuing investigation is to assess the potential for lode copper beneath the shallow waters surrounding the Keweenaw copper-producing district. Using Coast Guard ship support, approximately 1,000 track miles of (a) high resolution acoustic profiles, (b) intermediate depth air-gun seismic profiles, (c) continuous magnetometer records, and (d) some 200 dredge and grab samples of the bottom as well as coastal sediments and sub-lake rock exposures were collected. Subsequent to the cruise, the geophysical records have been under study, and all sediment and rock samples have been analyzed for copper, zinc, cobalt, tin, and nickel.
The mapped distribution of copper values, and to a lesser extent zinc, cobalt, nickel, do resemble haloes similar to those found around some producing districts on land and are encouraging. On the north side of the Keweenaw Peninsula, the copper trend is parallel to the coast, while on the south side, the copper anomalies extend normal to the coast.
Based on preliminary interpretations of the geophysical and chemical data, we have identified three areas which warrant core testing as potential ""prospect,"" or interest, sites. These are: (1) the central, offshore area south of the Keweenaw centered on the filled trough, as determined by acoustical profiling, (2) the passage between the terminal end of the Keweenaw Peninsula and Manitou Island, where there is evidence of faulting, and (3) the shoaling approach to Stannard Rock, on a projected line between Keweenaw Point and Stannard Rock.
Selection of these areas of prospect interest has resulted from the preliminary survey of 1971, and while this represents only a first year assessment of a four-year exploration program, we are encouraged to conduct sub-bottom rock coring at these sites in 1974.
In addition to the exploratory aspects, we are also considering the environmental factors. Wisconsin personnel are much concerned that timely measures be taken to safeguard the lake environment, including aquatic life. Accordingly, we have assured those in the environmental awareness groups that we will continue to support clean exploration and exploitation underwater minerals operations. Moreover, chemical and bathymetric data collected at this time prove an environmental quality baseline in the event of subsequent mining.
Introduction
The Keweenaw Peninsula is renowned throughout the world as a classic mining district for the production of native copper, especially in the late nineteenth and first half of the twentieth centuries. With the increasing demand for copper material and the uncertainty of satisfying this demand from abroad, new emphasis must be placed on exploration within North America. Consequently, the principal objective of this continuing investigation is to assess the potential for lode copper beneath the waters of Lake Superior adjacent to the Keweenaw Peninsula.