B-04 Geology and Ore Deposits of the Monarch District and Tomichi Districts, Colorado


Geology and Ore Deposits of the Monarch and Tomichi Districts, 1913, by R.D. Crawford. 317 pages. 25 plates. 15 figures. Digital PDF download. B-04D

Excerpted from the introduction:

The Monarch mining district is in the southwestern part of Chaffee County, Colorado, on the east slope of the Sawatch Range whose crest forms a considerable length of the Continental Divide. The Tomichi district, in Gunnison County, joins the Monarch district on the west and is on the west slope of the range. The tract surveyed has an area of 120 square miles. That part east of the divide, 94 square miles, is all in the Monarch district excepting a small area at the head of Pomeroy and Grizzly gulches, which lies in the Chalk Creek mining district. The Monarch district is commonly understood to extend much farther south and southeast than the limits of the accompanying maps. Little development work has been done in the unmapped area, though at Pass Creek, several miles southeast of Maysville, a small amount of gold was found, and a group of prospects south of Greens Gulch has produced a few tons of ore.

The Tomichi mining district, as mapped, covers 26 square miles. This includes all the producing area of the district, although a little prospecting has been done farther west. The mineralized zone extends north into the Quartz Creek district which joins the Tomichi district along the divide at the head of Tomichi Creek.

The topographic and geologic mapping of the Monarch and Tomichi districts was completed during the summers of 1909 and 1910. Photographs of the area taken during the field work are included in the report, along with details of the mines of the districts, claims, and mine maps.

The report is organized into the following chapters: Introduction; Chapter I. Physiography and Quaternary deposits; Chapter II. Outline of geologic history; Chapter III. Pre-Cambrian rocks; Chapter IV. Paleozoic sedimentary rocks; Chapter V. Post-Carboniferous igneous rocks; Chapter VI. Structural geology; and Chapter VII. Local geology; Chapter VIII. Petrography of the post-Carboniferous igneous rocks; Chapter IX. Economic geology of the Monarch district; Chapter XI. Economic geology of the Tomichi district.