Abstract

The Silver City-Santa Rita region, in which are exposed rocks of early Tertiary age and older, is located within a block bounded by the northwest trending Mimbres and Silver City faults.The Santa Rita granodiorite intrusive is about 6,200 feet long in a northwesterly direction, and averages 2,600 feet in width. It is flanked on its east and west sides by limbs of a south-plunging anticline. The granodiorite-sediment contact is nearly vertical over a good part of the east and west sides of the intrusive and plunges to the north at an angle of about 40 degrees. The anticlinal structure extends to the north where superimposed upon it are found at least three smaller flexures, domes and anticlines; zinc ore bodies are found in the upper portion of these structural highs.There are no indications to date that the intrusive has a bottom. Its emplacement seems to have been a passive one followed by a downward readjustment in the north end of the mass. Other than an uplift of the sediments to form the anticline, there are no indications that the intrusive pushed or thrust the sediments aside such as the pushing or thrusting that apparently accompanied the Fierro-Hanover and Copper Flat intrusives.It is conceivable that this difference in the mode of intrusion may account in part for the shattering of the rocks, which was so important for the formation of the copper ore bodies in the Santa Rita intrusive and is lacking in the Fierro-Hanover and Copper Flat intrusives.

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