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The AAPG/Datapages Combined Publications Database

Rocky Mountain Association of Geologists

Abstract


The Mountain Geologist
Vol. 46 (2009), No. 1. (January), Pages 13-25

The Coal Geology and Mining Resources of the Boulder-Weld Coal Field

Christopher J. Carroll

Abstract

From 1859 through 1979 coal mines in the Boulder-Weld Coal Field produced over 109 million short tons of coal from the Maastrichtian Laramie Formation. Over 221 million short tons were depleted from an estimated remaining reserve of 1.13 billion short tons. The mineable or recoverable reserve portion of that is calculated at 557 million short tons. Most of the subbituminous to bituminous coal was mined by underground shaft methods but was limited by a pervasive horst and graben fault system. For the towns of Louisville, Lafayette, Erie, Superior, Dacono, and Frederick, Colorado, coal mining will always be a part of their history. These towns were created by mining, and urban growth has subsequently developed around and over subsiding ground: Future coal mining is significantly hindered by these technological and urban land-use restrictions.

The Late Cretaceous Pierre Shale, Fox Hills Sandstone, Laramie Formation, and the Paleocene Arapahoe Conglomerate represent bedrock exposures in the Boulder-Weld Coal Field ranging in age from approximately 70 to 64 Ma. Together these formations record the last regression of the Cretaceous Seaway and the beginning of the Front Range Uplift. The term Laramide is derived from stratigraphic and structural elements of the Laramie Formation found in the Boulder-Weld Coal Field. The two divisions of the Laramie Formation represent two different depositional environments on a coastal plain: the upper unit has shale with thin interbedded sandstone beds on an alluvial coastal plain, while the lower unit contains sandstones interbedded with coal and kaolinitic clay beds depicting a near-shore coastal or delta plain marked by fresh to brackish-water environments favorable for coal development. The complex system of facies developed includes shoreface sands with associated longitudinally-oriented coal mires, abandoned distributary channels truncating coal beds, with splays and levee complexes with channel switching in a poorly drained environment.


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