The Bundarra project consists of a granted
Exploration Permit for Minerals (EPM 11613) that covers an
area of approximately 200km2. The project lies 120km southwest
of Mackay in the Bowen Basin of central Queensland. A rail
line between the Bowen Basin coalfield and the coast passes
less than 10km to the north of the tenement. Access from
Mackay is by the Sarina/Marlborough Road, then via the Peak
Downs Highway and Fitzroy Road to Bundarra Homestead. A
network of formed gravel roads provides good access within the
tenement.
The project area covers numerous genetically
related (epithermal) copper-gold occurrences located around
the perimeter of a large granodiorite intrusion known as the
Bundarra granodiorite. Copper and gold mineralisation
typically occurs as discrete lodes or breccias within contact
metamorphosed sediments. Historically, copper was produced
from the numerous small mines in the late 1800s, and 1960s.
Modern exploration commenced in the early 1960s and
was carried out sporadically through to the late 1980s,
outlining further areas of mineralisation and confirming the
area’s potential to host multiple styles of mineralisation,
including; 1) high-grade copper-gold vein type mineralisation
amenable to open pit and underground extraction, 2) bulk
tonnage low grade or smaller higher grade breccia hosted
gold-copper bodies, and 3) bulk tonnage low grade sheeted
vein/stockwork copper-gold bodies.
A review of past
exploration suggests that limited work is required to
delineate copper-gold resources at a number of prospects, and
that the project area is also prospective for large IOCG
copper and gold systems of Olympic Dam and Ernest Henry style.
In the past, exploration of the Bundarra region was hampered
as a result of competitive company attitudes and fragmented
tenement ownership, however Regency now has complete tenement
coverage over the entire Bundarra pluton (and its margins),
enabling systematic evaluation of all prospective areas.
Click on image for full graphic  Bundarra Aeromagnetics and
Radiometrics
Regional Geology and
Mineralisation
The Bundarra tenement
covers the oval shaped Early Cretaceous Bundarra Granodiorite
pluton, which intrudes sedimentary rocks of the Lower Permian
Back Creek Group, part of the Bowen Basin. The pluton is
approximately 6km x 14km in size. The granodiorite pluton is a
composite body with phases ranging from diorite, quartz
diorite, monzonite, adamellite, through to alkaline granite
and syenite. In the south western part of the pluton complex
is the Painted Peak pluton, which is readily discernable as a
separate intrusion on airborne magnetic data. It is dominated
by porphyritic dyke swarms and is possibly emplaced at higher
level than the remainder of the complex. Outcrop is relatively
poor so the intrusive relationships between the various phases
are not known. Microgranite/microsyenite dykes and sills
intrude the sedimentary rocks to the west and south of the
Bundarra Granodiorite.
Intrusion of the pluton is
interpreted to have been localised at the intersection of two
regional lineaments, one a northwest-trending zone defined by
several other Cretaceous intrusions located along the axis of
the Bowen Basin, and the other a northeast-trending lineament.
The surrounding Permian sedimentary rocks are
predominantly fine-grained silty carbonaceous rocks, domed
upwards because of the granodiorite intrusion, and dip at 20°
to 50° radially outwards from the pluton. These sedimentary
rocks have been metamorphosed and altered to upper
albite-epidote facies metasediment, locally containing knotted
andalusite, in an aureole up to 800m wide along the pluton
contact.
The altered silicified rocks are more
resistant to weathering and so form a prominent topographic
rim around the perimeter of the pluton. Alteration is very
extensive as can be seen on airborne radiometrics and
magnetics. A prominent positive response on airborne magnetic
data has been attributed to the development of
pyrrhotite/magnetite/hematite, and a high coincident potassium
channel radiometric count has been attributed to abundant
potassic (biotite/?K-feldspar) alteration, in addition to
silicification.
The discovery of many copper
occurrences within, and surrounding, the pluton led to the
proclamation of the Mount Flora Mineral Field in 1907.
Historically copper was produced from numerous small mines
from the late 1800s to 1909, when production decreased due to
the failure of the local smelter. Records indicate that
between 1900 and 1918, 1,930 tonnes of ore were treated at an
average grade of 16.5% Cu. Between 1909 and 1920, and again
during the late 1960s and early 1970s, production from the
more significant Mt Flora and Mt Orange deposits was sent to
Mt Morgan for treatment. Production from the Isens Mine in the
Mt Orange area in the 1960s-1970s is said to total 10 000t
grading 8-12% copper, 6-9 oz/t silver, and 2g/t gold.
Two main and distinct styles of mineralisation have
been recognised within the area: quartz-hematitecopper-gold
vein deposits located close to the margin of the pluton,
either within or immediately adjacent to the granodiorite, and
copper-gold breccia or stockwork deposits hosted within the
metasediments peripheral to the granodiorite. Almost all of
the old workings are situated within 2 to 6m wide fracture
zones. Higher grade lodes within these zones are generally up
to 1m wide and commonly exceeded 15% Cu. The fracture zones
are usually perpendicular to the contact between the
granodiorite and the sedimentary rocks, although some are
parallel to it. Surrounding these fracture zones, particularly
in the Painted Peak area, are zones of alteration up to 90m
wide. The alteration is generally not of a pervasive nature
but more commonly consists of anastomosing fractures.
Alteration minerals are generally hematite, silica, sericite,
chlorite, K-feldspar, and rare magnetite.
Mineralisation consists of copper carbonates and/or
copper sulphides and gold in a gangue of quartz, hematite,
pyrite, pyrrhotite and more rarely magnetite. Magnetite
occurs, for example, at Rogers prospect as bladed crystals
pseudomorphed after specular hematite, and at the Clooracorn
mine and Painted Peak as hematite-magnetite veining in
breccia. Magnetite also occurs in association with quartz-K
feldspar dykes which are commonly intrusive into breccias.
Vein mineralisation in the granodiorite can have
strike lengths greater than 500m. Disseminated sulphides can
occur between multiple sheeted veins. The known breccia style
deposits are scattered in the Painted Peak-Rogers-Isens- Hill
1 areas.
The largest breccia system is at Quorn. Here
brecciation has a surface area of 150m x 75m and is surrounded
by an alteration envelope of 250m x 125m. It is a collapse
breccia in black siltstone and contains large clasts (up to 2m
wide) of quartz/potassium feldspar altered porphyry. A
stockworkedquartz feldspar dyke intrudes the breccia-wall rock
(siltstone) contact.
Previous
Exploration/History
Historically, a
systematic coverage by exploration and mining groups has been
hampered by a fragmented tenement ownership and restrictions
in gaining access to areas under freehold title. Regency now
has complete tenement coverage over the entire Bundarra pluton
and its margins. The first phases of modern exploration of the
Bundarra area occurred from 1963 to 1973, focusing especially
on the potential for intrusive-related porphyry-style copper
and gold mineralisation. In this period, Enterprise
Exploration Pty Ltd, Geopeko Limited, Planet Metals Limited,
Shaw River Alluvials Limited, ICI Exploration, and the
Endeavour Oil Company carried out geological, geochemical,
geophysical, diamond drilling and mine evaluation programs at
Mount Orange and Mount Flora. In 1973 Endeavour Oil calculated
that the mineralised body at Mt Flora consisted of 262,000t at
2.59% Cu and 40g/t Ag, with possibly up to 1.45Mt.
In the early 1980s Chesterfield Mining and Exploration
evaluated the Quorn breccia and other occurrences along the
northern margin of the granodiorite, with the best result from
drilling being 3m at 7.25g/t Au at the Cadet Prospect. In
1984, Carpentaria Exploration Pty Ltd completed a gravity
survey over the area. This work outlined a strong gravity
ridge along the western edge of the intrusive which was
interpreted as another intrusive, or a stacked set of hematite
veins within the Permian sediments.
Between 1986 and
1988 G.S.S. Homes Pty Ltd, ARI Ltd and Elliott Exploration Co
Pty Ltd evaluated targets at Mt Flora, Quorn and Painted Peak
by reanalysing earlier drill holes for gold, and by costeaning
and rock chip sampling. Results included 6m at 2.2g/t Au and
6.5% Cu at Isens. In 1989 Xenolith Gold Ltd conducted
photogeological mapping, stream sediment sampling and rock
chip sampling south of the intrusive complex. Breccias (of
apparently limited tonnage potential) were located east of
Mount Orange, though at the Hill 1 prospect rockchip samples
returned up to 3g/t Au.
Paladin Resources Pty in
1989-1991 defined two copper-silver-gold prospects in the
Quorn area. Exploration comprised bulk leach and rock chip
sampling and detailed mapping. This was followed, between 1991
and 1994, with exploration efforts by Dominion Mining Limited,
Marlborough Mines NL, Queensland Metals Corporation, and
Normandy Exploration Limited over several areas, including the
Quorn Breccia. Here an 800m long siliceous breccia was located
containing up to 9% Cu, however results of drilling suggested
the better grades were confined to near surface, and that the
breccia narrowed at depth. In 1994, MIM Exploration Pty Ltd
re-processed and interpreted airborne magnetic data and
drilled targets on the northern margin of the intrusion,
however no results of significance were returned. In
2001,Central Queensland Resources Ltd drilled six Reverse
Circulation (‘RC’) holes at Mt Flora, intersecting up to 8m at
0.71% Cu.
Exploration Potential
Regency’s tenement covers an entire
mineral field in which there are numerous significant
disseminated, vein and breccia type copper gold deposits in
and adjacent to the Bundarra Granodiorite pluton. Two main
styles of mineralisation have been recognised within the area;
they are firstly copper-gold vein deposits located close to
the margin of the intrusion, hosted by either granite or
metasediment, and secondly copper-gold breccia or stockwork
deposits hosted within the meta-sediments peripheral to the
granodiorite.
The known main mineral deposits, in both
the metasediments and in the granite have been evaluated with
a variety of techniques including rock chip sampling,
costeaning, IP surveys and drilling. These were designed to
find strike and depth extents of the mineralisation. Existing
drilling on vein-style deposits suggests that high-grade
mineralisation may be discontinuous and that copper and gold
grades may be preferentially enriched in the near-surface
oxidised zone. However, the Mount Flora and Isens systems, for
example, have received limited drilling along the strike and
depth extent of the vein systems.
Furthermore there is
potential for broad zones of low-grade mineralisation
occurring as disseminated sulphides between multiple sheeted
veins as demonstrated by the Central Queensland Resources
drilling results.Therefore, it is considered that such targets
require further evaluation and exploration.
Breccia or
stockwork mineralisation is known at Quorn, adjacent to the
western margin of the pluton, and at the Hill 1, Hill 2 and
Hill 3 prospects that are located within the embayment in the
southern margin of the pluton. At Quorn the breccia contains
up to 9% secondary copper mineralisation at surface, with
grades not replicated by drilling. The breccia was interpreted
to be narrowing at depth, although this interpretation may be
incorrect because only limited percussion drilling has been
completed to date, and it is unlikely that the breccia could
be effectively logged in drill chips.The interpretation was
likely to have been based on the copper grade distribution,
which is an unreliable lithological indicator.
At Hill
1, gold analyses of up to 3g/t Au were obtained in rock chip
sampling, however no drilling was completed due to the low
tenor of soil anomalies and absence of observed strong
hydrothermal alteration. The exploration data suggest that a
more rigorous approach to exploration in this area is
warranted and that there is potential for large disseminated
gold and copper breccia systems. Breccia-style deposits have
generally been only modestly explored. No systematic approach
to geophysical or drilling programs has been adopted within
these prospects, and the existing drilling has generally been
targeted on the basis of limited geochemical data. It is
possible that breccias of Kidston/Mt Leyshon-type may occur in
the area; clearly these would be attractive targets.
In the Painted Peak region, there are many indications
that the intrusive is at a high level. The evidence includes
the presence of breccias, pebble dykes, porphyritic dyke
swarms, and open space comb-quartz lined vughs. There is
intense alteration over a large area. This is a potentially
highly productive environment for the development of
gold/copper mineralisation of several styles. The
metamorphic/metasomatic aureole around the pluton is up to
800m wide and airborne magnetics and radiometrics clearly show
that a vast volume of pyrrhotite/hematite/magnetite/ potassic
alteration is present. It is host to most of the known
mineralisation. Doubtless other copper/gold mineralised
systems apart from the known ones remain to be found in such a
large system.
The southeast margin of the pluton has
not attracted any recorded exploration, apparently due to
issues related to land access in this area. The south-eastern
margin of the intrusive includes an embayment similar to that
which hosts the Mount Flora lode system, providing an
immediate high priority target for exploration.
The
common presence of hematite (and magnetite) associated with
potassic alteration in the lodes is consistent with a model
involving the mixing of hydrothermal fluids (derived from the
granodiorite) with oxidised meteoric fluids. This model for
mineralisation is similar to other iron oxide-copper-gold
(‘IOCG’) systems that include a range of mineral deposit
styles from porphyry-copper through to large deposits such as
Olympic Dam and Ernest Henry. No systematic approach to
exploration for IOCG style deposits has yet been done, but is
readily justified.
In summary, the Bundarra Project is
considered to have the potential for 1) modest tonnage,
high-grade copper-gold vein type mineralisation amenable to
open pit and underground extraction, 2) bulk tonnage low grade
or smaller higher grade breccia hosted gold-copper bodies, 3)
bulk tonnage low grade sheeted vein/stockwork copper-gold
bodies, and 4) large IOCG systems of Olympic Dam and Ernest
Henry style.
Regency has high quality aerial
photography over the entire project area, and a digitally
compiled geochemical and drilling database of previous
exploration data. This information provides a basis from which
the nature and effectiveness of previous exploration can be
evaluated and new targeting strategies developed with modern
exploration techniques in mind. The company has proposed an
exploration program that includes the following key elements;
 Acquisition and processing of multi-spectral
satellite imagery, and further processing and interpretation
of airborne magnetic data.
Selection of target areas from data
compilation, and from interpretation of satellite imagery and
magnetic data.
Ground assessment of targeted areas, including
geological and structural mapping, and geochemical sampling.
Reconnaissance Rotary Air Blast (‘RAB’) drill
testing, potentially of the Mt Flora and Isens areas.
See also Bundarra
Assessment Note and Exploration Update – graphics version or Exploration Update – non-graphics
version
Based on an independent
geological report prepared by Baxter
Geological
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