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Detailed geological data from our current drill program can be found HERE.
A map of Keweenaw Copper Co. projects can be found HERE.
Copper in the Keweenaw
The copper-bearing rock sequence in the Keweenaw consists of several hundred lava flows with interbedded conglomerate and sandstone layers. The entire sequence is called the Portage Lake Lava Series (PLLS). Structurally, the series is the southeastern limb of a major syncline that dips down below Lake Superior. The northwest limb of the syncline is exposed on Isle Royale near the northwestern shore of Lake Superior. The rocks are Keweenawan in age (Upper Precambrian) and represent a sequence of flood basalts that can be traced in the subsurface several hundred miles to the southwest by means of their magnetic signature.
The lava flows are basaltic in composition, and the entire sequence is several thousand feet thick. Individual flows range in thickness from a few feet to at least 1,600 feet and in strike length from just a few hundred feet to at least 40 miles.
The base of Keweenawan basaltic flows is truncated by a major low- to high-angle reverse fault known as the Keweenaw Fault. The fault is generally parallel to the strike of the PLLS and thrusts these rocks over a younger red bed sequence named the Jacobsville sandstone.
Historically, three types of deposits were mined. Most spectacular were the fissure veins that hosted individual masses of native copper, often weighing hundreds of tons. More productive, however, were the native copper lodes in brecciated and scoriaceous amygdaloid flow tops and lode deposits in conglomerate horizons.
At the properties of interest, copper is hosted in at least three stratigraphic horizons. At the Centennial Mine, copper is contained within the Calumet & Hecla conglomerate, the most productive host in the district. At the Kingston Mine, copper is hosted in the Kingston conglomerate, a minor host in the district.
At the 543S and other copper sulfide deposits, copper is hosted mainly in amygdaloid flow tops and rarely in conglomerate in basal units of the PLLS.
Native copper and associated native silver were generally associated with calcite, quartz, epidote, and chlorite; frequently with prehnite, datolite, analcite, and laumontite; and uncommonly with apophyllite. Rock alteration in the dense trap rock is not extensive; the most common alteration minerals are reddish adularia feldspar, chlorite, epidote, pumpellyite, and laumontite. In the northern area sulfide deposits, the primary copper mineral is chalcocite, with minor amounts of native copper and silver. Alteration is similar to alteration at the native copper mines.