NI43-101Pre-Feasibility Study Report - page 121

Rare Element Resources
Bear Lodge Project
Canadian NI 43-101 Technical Report
October 9
, 2014
10135-200-46 - Rev. 0
Syenite: Syenite is interpreted to be the coarse
grained equivalent of the
trachyte/phonolite porphyry unit, and some variations are gradational with it. The unit
includes syenite, nepheline syenite, and microsyenite lithologies and their porphyritic
equivalents. Syenitic rocks are light to medium grey and range from fine grained
(microsyenite) to medium or coarse grained. They are composed of alkali feldspar ±
subordinate nepheline, biotite, clinopyroxene, alkali amphibole, hornblende, sphene,
olivine, magnetite and pyrite. Allanite, apatite, pyrrhotite, and ilmenite may be present
rarely as accessory phases. Syenitic rocks are often carbonate
flooded with calcite
microveinlets and patchy calcite replacement of phenocrysts and groundmass below
the zone of oxidation.
Lamprophyre: Lamprophyric rocks can occur both early and late in the intrusive
sequence. They are dark grey to black and fine grained. They contain a variable
assemblage that may include biotite, pyroxene, alkali feldspar, nepheline, and/or
sulfides, and mafic mineral abundances may exceed 50 percent. Sulfide mineralogy is
principally pyrite, and magnetite is a common accessory. Carbonate can occur in
ocellar patches in association with apatite. The lamprophyres occur in dikes and in
local intimate association with syenite. Lamprophyre dikes intrude the Bull Hill
7.3.2 Alteration
Hydrothermal alteration identified in the Bear Lodge alkaline
igneous complex is
dominated by K
pyrite alteration and/or fenitization (alkali
ferric iron
metasomatism). Carbonate alteration is common, but not as widespread as the
potassic alteration. Carbonate is leached from many surface exposures during
supergene oxidation of pyrite. Minor amounts of argillization, sericitization, and
silicification are noted locally.
The greatest concentration of REE
mineralized carbonatite dikes and veins occurs
in the vicinity of the Bull Hill diatreme. Beneath the oxidation zone, the heterolithic
intrusive breccias of the Bull Hill diatreme are characterized by a variety of alkaline
igneous clasts in a matrix of K feldspar, biotite, carbonate, and pyrite. Carbonate is
largely absent within the zone of supergene oxidation, apparently replaced by silica
and limonitic FeOx. Sulfides are strongly oxidized to limonite ± hematite, and
biotite/phlogopite exhibits variable moderate to strong oxidation, as well. It is
difficult to discriminate alteration related to the intrusion of the carbonatitic bodies,
although stockworks of hairline calcite veinlets and patchy replacement of K
feldspar and biotite may be related to the carbonatite intrusions. Many of the clasts
are carbonate
flooded and some exhibit pyritic reaction rims. Fenitization (alkali
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