bgf equities says byr is a hold for results , page-32

HC, Ernest Henry starts around 50m below surface, still very shallow for IOCGU standards.


A genetic story for the Ernest Henry IOCG deposit
Stephen Twyerould, Consultant



The Ernest Henry deposit is a Proterozoic iron-oxide-copper-gold (?IOCG?)
deposit with a pre-mining resource of approximately 170 Mt @ 1.1% Cu and 0.5
g/t Au. The deposit mineralization is fairly representative of this class of IOCG
deposit. Genetic models must take into account the specific textural, geological,
mineralogical and chemical characteristics of the deposit. These genetic models
can then be applied to similar deposits, with implications for exploration.
The deposit is located in the Mt. Isa Inlier, NW Queensland, Australia and is
covered by approximately 50 m of overburden. It consists of a 50o southeast
plunging, pipe-like body of breccia lenses, bounded by shear zones. Regional
sodic alteration formed during and after the development of the shear zones and
peak metamorphism. This was followed by intense potassium metasomatism
(red-rock alteration). Brecciation and Cu-Au mineralization formed after the bulk
of red-rock alteration. The main mineralized breccia consists of a magnetite-rich
matrix containing ore minerals surrounding potasic altered clasts. Textural and
geochemical evidence indicates strong host rock dissolution during the
mineralizing event.
Copper correlates strongly with iron, nickel, gold, uranium and molybdenum but
less strongly with, arsenic, bismuth, cobalt, lead and antinomy. Whole rock
analyses, mass balance calculations and textural evidence indicate that the ore
breccias formed by replacement of the host rock. Replacement probably
occurred at or near constant volume.
Thermodynamic and stable isotope studies indicate that mineralization formed
around 450 ? 50oC from a magmatic or deep crustal fluid. Geochemical
modeling suggests that this fluid was reduced, moderately acidic, saline, sulfurdeficient
and carried significant amounts of Fe, Cu and F. Reaction of this fluid
with the red-rock altered host rocks is the most likely mechanism for the
formation of the deposit.