Exploitation of tungsten orebodies in a silver-lead district has revealed new data, in conflict with published accounts of Darwin ore genesis. Knopf's assignment in 1913 of pyrometasomatic origin was contested by Kelley, who, in 1937, suggested mesothermal classification. A high-temperature formation of scheelite is indicated by its intimate association with wollastonite and marks the earliest epoch of metallization. Mineralization is channeled by fractures into receptive sediments, and forms replacement lodes. Veins, faults, and fissures, first mapped by Kelley and analyzed by their frequency and magnitude of occurrence, are defined as systems forming a pattern of tear lines and tension fractures. Regional continuity of the former supports a concept of tectonic development rather than local origin confined to the influence of the Darwin intrusive.The extensive development of scheelite ore shoots since discovery in 1940 maintains a reserve approximating 25,000 tons, with other estimates of available ore varying to 70,000 tons. The study and analysis of ore foci suggests potential reserves of several hundred thousand tons, which warrants substantiation in order to justify installation of a mill within the district. The latter will eliminate current tendency toward selective mining which results in loss of greater potential production of vital metal.

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