NI43-101Pre-Feasibility Study Report - page 114

Rare Element Resources
Bear Lodge Project
Canadian NI 43-101 Technical Report
October 9
, 2014
10135-200-46 - Rev. 0
7 Geological Setting and Mineralization
7.1 Introduction
This section discusses the geology and mineralization of the Bear Lodge property
based on the most recent geological and mineralogical data derived from work
conducted on the property through 2013.
7.2 Regional Geology
The Bear Lodge Mountains of northeastern Wyoming are part of the Black Hills Uplift,
formed during the Late Cretaceous-Tertiary Laramide Orogeny. The uplift has a
northwesterly orientation and extends from the western South Dakota – Nebraska
border through northeastern Wyoming into southeastern Montana. The exposed
basement consists of Precambrian schist, gneiss, and granite overlain by Paleozoic
and Mesozoic clastic and carbonate sedimentary rocks that were subsequently
eroded from higher elevations. The Paleozoic and Mesozoic rocks were subjected to
large-scale monoclinal folding that encircles the Black Hills Uplift. Younger Oligocene,
Miocene, and Pliocene sediments disconformably overlie the older sedimentary and
igneous rocks at lower elevations of the uplift (Figure 7.1).
Tertiary alkaline intrusive bodies in the northern Black Hills are located along a N70-
80W trending belt that extends from Bear Butte in South Dakota, through the Bear
Lodge Mountains, to Devil’s Tower and Missouri Buttes in northeastern Wyoming
(Figure 7.1). The alkaline igneous rocks generally transition in composition from
silica-saturated to silica-undersaturated from southeast to northwest. Potassium-
argon age dates of the Tertiary intrusive rocks range from 38 to 60.5 Ma (Lisenbee
1985), with younger intrusions more common toward the northwestern end of the belt
(Figure 7.1). Isolated anticlinal domes are dispersed throughout the region and are
probably cored by alkaline igneous plugs of Tertiary age. On a broader scale, the
Bear Lodge intrusive complex and other Black Hills alkaline igneous bodies are part
of a northerly trending belt of scattered alkaline-igneous systems that occur from
Mexico to Canada, several of which are associated with significant gold deposits
(e.g., Cripple Creek in Colorado, the Zortman-Landusky complex in Montana, and the
Carache Canyon breccia pipe in New Mexico).
Aside from the Bear Lodge intrusive complex, only the Gallinas Mountains complex in
New Mexico is known to host carbonatite associated with significant rare earth
occurrences along this belt.
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