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Moderate: Low: Weak: Strong development of one of the destructive processes (or moderate development of two) and weak to moderate development of at least one more. Rocks may or may not be strong enough to hold a back, depending upon which destructive processes have been active. Strong development of argillization or fracturing would make the rock very weak or unstable, whereas strong development of oxidation or leaching may not seriously affect its ability to hold a back. Moderate leaching with only minor other effects. The compressive strength of the rock is not seriously reduced. Weak development of leaching and/or oxidation. Rock strengths are not affected. GENERALIZED ILLUSTRATIVE CROSS SECTION Figure lA is a generalized cross section illustrating a typical north-south weathering profile of Crandon deposit rocks. From this profile, basic weathering characteristics which apply throughout the deposit can be illustrated and discussed from figures 1B-1F. The weathering profile and active destructive processes vary considerably between footwall, Crandon formation and hanging wall. This is in response to the primary chemistry of the rocks, and the physical-chemical conditions acting upon those rocks. -3-
In discussing the generalized cross sections, it must be kept in mind that they represent basic weathering characteristics and principles applicable at this deposit. The fact is that the supergene weathering system is very complex and has many irregularities and variations from the generalized norm. While the base of the weathering zones are shown relatively smooth on the generalized section for illustrative purposes, in reality they are shaped much like the base of a nolar tooth, with many root-like projections. Two types of ore are present at the Crandon deposit. Massive ore is a zinc-rich syngenetic ore type which is contained strictly within the Crandon Unit. Stringer ore is a copper-rich epigenetic ore type which is contained within the footwall. It is important to remember that only portions of the Crandon Unit and footwall are of sufficient width and grade to be of commercial value. Footwall The footwall rocks follow a relatively uniform weathering pattern compared to the Crandon formation (Figure 1A). The lower boundaries of the various weathering intensities are relatively horizontal, but contain many root-like zones which penetrate deeper. The footwall weathering follows a relatively uniform pattern because the rocks are relatively uniform in compo.sition, being siliceous in nature. The primary destructive process is leaching. In the strongly weathered zone, strong leaching has reduced the competency of the rocks to the point where crushing and collapse has played an important role in physically breaking up the rock. The acidification of groundwater due to the breakdown of sulfide minerals has further caused the breakdown of silicate minerals, putting some into solution and altering others to clay products. -4-