NI43-101Pre-Feasibility Study Report - page 118

Rare Element Resources
Bear Lodge Project
Canadian NI 43-101 Technical Report
October 9
, 2014
10135-200-46 - Rev. 0
The Bear Lodge complex consists predominantly of silica
undersaturated alkaline
igneous intrusive rocks, and it is the only intrusive series in the alkaline belt where
associated carbonatitic intrusions are found. The high
level nature of the Bear Lodge
complex is confirmed by the presence of sparsely scattered outcrops of vesicular
lavas and coeval pyroclastic deposits in the northern Bear Lodge Mountains.
Recognizable hydrothermal alteration includes pervasive fenitization (alkali
ferric iron
metasomatism), K
pyrite alteration, minor silicification, and localized argillic
alteration, along with superimposed surface weathering and oxidation. Structural
mapping and interpretation are hindered by thick soil cover and lack of outcrop.
However, geophysical surveys (magnetics, radiometrics, and IP/resistivity) confirm the
limited field data that indicate a predominance of both northwesterly and east
northeasterly structural trends.
7.3.1 Tertiary Igneous Intrusions
The Bear Lodge alkaline intrusive complex contains multiple intrusions as plugs, sills,
and dikes of trachyte and phonolite porphyry, with lesser amounts of syenite, latite,
nepheline syenite, pseudoleucite porphyry, malignite, pyroxenite, lamprophyre, and
stage carbonatite and silicocarbonatite, and the complex is penetrated by a
variety of intrusive and diatremic breccia bodies. The core of the complex consists
primarily of subvolcanic phonolite and trachyte porphyry, with subordinate syenite,
nepheline syenite, and pseudoleucite phonolite porphyry. Carbonatite exposures occur
only on the upper southeastern flank of Carbon Hill. The alkalic rocks penetrated
Precambrian granite and gneiss, and were intruded as plugs, dikes, and sills into the
superjacent Paleozoic sedimentary rocks. The Bear Lodge complex may have been
laccolithic in form but after deep erosion, only vestiges of sedimentary-hosted
intrusive sills remain in the periphery of the dome and the core is all intrusive rock.
Numerous intrusion and intrusive breccias occur within the complex, and four
diatremes are identified. The intrusion breccia bodies consist of a phonolitic to
trachytic igneous matrix carrying varying proportions of cognate clasts, as well as local
minor syenite and/or lamprophyre clasts. In contrast to the intrusion breccias, the
heterolithic intrusive breccias contain abundant clasts of phonolite
trachyte, with
subordinate syenite, and lamprophyre in a fine
grained carbonate
K feldspar
sulfide matrix. The sulfides are oxidized in surface exposures, and the carbonate is
dissolved and replaced by silica and iron oxides. The Bull Hill and Carbon Hill
diatremic breccias are the most prominent examples of the heterolithic intrusive
breccias. Carbonatite and silicocarbonatite dikes intrude the heterolithic breccias and
are late in the igneous sequence. Lamprophyre, pseudoleucite phonolite porphyry,
and latite dikes are also late in the intrusive sequence. Most of the rock units are
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