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GROUNDWATER NEAR THE DETROIT CITY NOI <br /> GEOLOGY <br /> All of the prospects in the vicinity of the proposed Detroit City decline, as well as the decline itself, are <br /> hosted in Precambrian-aged crystalline basement rocks. Volumetrically minor dikes of Tertiary <br /> porphyritic intrusive rocks intrude this sequence locally, and are pre-mineral in age. Perhaps the best <br /> general term for the host rock lithology would be granite gneiss,with local migmatite, amphibolite, <br /> biotite schist and other lithologies present. The closest nearby rocks that could conceivably host <br /> formational water(perched aquifers, karst- related pools or intergranular pore space water) lie <br /> nonconformably on top of these basement rocks more than 1000' above the proposed decline (the <br /> Paleozoic section) and will not be penetrated. Even so, there are no workings above the mine in the <br /> Paleozoic section making water presently,to the authors knowledge. <br /> This part of the Alma Mining District is transversed by a complex, intersecting network of faults,joints <br /> and veins with prevalent strikes of NE, NNW and E-W. All structures show steep dips of 60 degrees or <br /> more. These structures tend to be open, as indicated by the fact that they controlled not only the vein <br /> emplacement, but the emplacement of intrusive rocks prior to the veins formation. The veins <br /> themselves tend to be vuggy and open, hence the potential for crystallized pockets of minerals that are <br /> the focus of this project. The Precambrian here (frequently termed the Idaho Springs Formation) is thus <br /> a competent, brittle unit capable of sustaining open, steeply dipping fractures, faults and veins. This <br /> interconnected set of open structures is an effective drain for the side of Mt. Bross pictured. <br /> NOTES ON INDIVIDUAL NEARBY MINE WORKINGS (see attached figure) <br /> Upper tram adits-these open tunnels have occasional standing puddles, but no discharge, and are <br /> situated more than 500' above the proposed adit. They explored the same vein system which this <br /> project intends to develop from below and to the south. <br /> Blaine sublevel lower adit-developed the large Blaine vein system and are caved. There is no <br /> discharge present at portal, more than 400' above the proposed adit. <br /> Sara Rose adit-this currently permitted and active minesite is well north of, and more than 500' above <br /> the proposed tunnel. Again, there is no discharge from the portal. <br /> Corkscrew adits (2)-these working are adjacent(120' north at same elevation to main adit)to the <br /> proposed adit, and are dry. The lower Corkscrew was rehabbed in the 90's and the author mapped <br /> several hundred feet of drifts, etc. at that time. Not even standing water was present. <br />