afternoon read, page-2

Indeed note :

Grasmere Copper and Gold
Mineralisation
High-grade secondary copper minerals
were mined at Grasmere during the late
1800s to early 1900s. Primary Cu, Zn
and precious metal mineralisation
occurs along a line of quartz and
magnetite lode with some 4 km of
outcropping strike length. Drilling
results indicate a continuous, steeply
dipping, primary massive sulphide lode.
The lode dominantly consists of
pyrite with lesser chalcopyrite and
sphalerite, occurring down dip from
siliceous and ferruginous gossans with
secondary copper minerals. Better drill
results include: 6.10 m @ 2.73% Cu;
0.64% Zn; 6.0g/t Ag and 0.21 g/t Au and
8.50m @ 2.95% Cu; 0.71% Zn; 6.8 g/t
Ag and 0.02 g/t Au. Typical results with
estimated true width sulphide
intersections are: 1.6 m @ 3.54% Cu
and 3.3g/t Au (61.4-63 m), and 3.6 m
@ 3.78% Cu, 1.12% Zn and 0.16g/t Au.
Although limited exploration has
been conducted along the 4 km strike
length of exposed Grasmere lode, most
drilling undertaken by previous
explorers has concentrated on a 400 m
longitudinal section of the lode. The
recent mapping project has identified a
prospective horizon extending beyond
the exposed lode to the northwest and
southeast, greatly enhancing the
prospectivity of the area. At map scale
outcrops of the gossan appear to
transgress the mapped local stratigraphy
of interlayered tuff, quartz magnetite
rock and magnetite, epidote and pyrite
altered basalt of the Grasmere beds. In
drill core the lodes are finely banded,
suggestive of syngenetic origin. The
lodes may therefore be simply
transposed and upgraded by later
en echelon fault movement. Fault
movement is evident at the sharp,
sheared sulphide lode margins and at
outcrop and map scales.
Further Exploration Potential
Other notable prospective areas are a
group of pits and shafts sunk into copper
and gold-bearing fault breccias at
Rawlins Tank and pits and alluvial
workings where Prospectors Creek
crosses the Koonenberry Fault. Other,
possibly prospective areas include a
three metre deep shaft with a drive of
indeterminable length developed within
the basal conglomerate member of the
Pevril Peak outcrops of the Devonian
Snake Cave Sandstone. A grab sample
of mullock returned anomalous values
of 0.044 ppm Au and 13.0 ppm U.
Dilational zones adjacent to the
Koonenberry Fault are also a valid
target for lode gold deposits and
possible Cobar-style structural traps.
A grab sample taken from an
unprospected gossanous quartz vein
returned an assay of 0.33 g/t Au,
1.5 ppm Te and 118 ppm Co. Also
previously undocumented are numerous
shafts developed within quartz and
epidote altered basalt of the Paddys
Creek beds.
Within the Mount Daubeny Basin
(see page 21), Late Silurian-Early
Devonian red-bed dominated sediments
and contemporaneous volcanism occur.
The development of volcanism in a
rapidly subsiding basin occurs in
response to high heat flows in stretched
and attenuated basement rocks and
provides the ideal mechanism for the
development of intrusive related
mineralisation. Within or immediately
adjacent to the Mount Daubeny
Formation on the adjoining Kayrunnera
1:100 000 sheet lie the Nuntherangie
Silver field (Pb, Ag), Wertago Copper
field (Cu +/- Au) and Great Wertago
Mines (Cu). Epithermal gold and
porphyry copper systems are possible
in such an environment.
This article is based on a paper presented
by Peter Buckley at the 2000 BHEI
Conference, with an abstract published in
AGSO Record 2000/10.
For further information contact Peter
Buckley on (08) 8080 0632,
fax (08) 8087 8005 or e-mail:
[email protected]