History
Secondary copper mineralisation was discovered and evaluated by prospectors using hand-dug trenches in the 1940s.
The first significant exploration was conducted by Texins in 1969 under Authority to Prospect (ATP) 568. Texins flew an airborne scintillometer survey over a major portion of the Wonga Sub-province with ground follow up by stream sediment sampling. At Kalman they conducted detailed geologic mapping and soil geochemistry over the Kalman line and drilled eight diamond holes.
PIMEX explored the northern half of the Kalman line from 1988 to 1992 under ATP 4423 and then Mining Lease (ML) 2765. As the majority of their work was conducted under the ML there are no public records of their exploration after the first eight drill-holes. PIMEX completed soil geochemistry and self-potential surveys. The soil geochemistry identified a strong copper anomaly (7500 ppm Cu) flanking the quartz vein and overlying areas of black shale. The anomaly was terminated sharply at the northern end. Drilling identified a number of narrow mineralised copper/gold/molybdenum lodes within 100 m of surface.
MIM conducted exploration over the southern portion of the Kalman line between 1990 and 1993 under EPM 5159. They completed an extensive soil geochemical survey followed by diamond and RC drilling at the Kalman, Pelican and Pelican South prospects. The soil geochemistry identified a zone of anomalous copper geochemistry extending for 5 km along strike. MIM drilled 10 diamond holes for 2079 m into a number of priority targets defined by the geochemical survey. This was then followed by a second phase of RC drilling consisting of 22 holes for 2613 m.
Cerro Resources commenced reconnaissance work at Kalman in July 2005. The first drill program of four RC holes was completed in October 2005. This was followed in March 2006 by another four RC holes which were later extended by diamond tool in May-June 2006. A further 49 diamond holes and 55 RC holes were drilled from October 2006 to December 2009. In addition detailed mapping and soil geochemistry has been completed over 20 km of the Pilgrim Fault zone from China Wall south to Serendipity.
A total of 47.7 kilometres has been drilled in the Mount Isa Project in the period 2005-2010, the majority of which has been drilled into the Kalman Deposit.
Geology
Geological Setting
The Mt Isa Project area straddles the Wonga Sub-province of the Eastern Succession. The Kalman Deposit is located adjacent to the Pilgrim Fault Zone, a major crustal suture transecting the Mount Isa Inlier that separates the Wonga Sub-Province from the Ewan-Malbon Sub-Province. In the vicinity of Kalman the fault abuts the Corella Formation against Overhang Jaspillite. From deep seismic transects the Pilgrim Fault is interpreted as an east dipping listric fault with a surface expression of multiple, stacked, east stepping, steeply west dipping shears.
Regional Geology
Stratigraphy
The Kalkadoon Granodiorite is regarded as local basement. It is described as a coarse to medium grained granite with granodiorite, leucogranite, aplite and gneiss. It is Palaeoproterozoic in age and outcrops in the western portion of the project area within the Kalkadoon Ewan Province.
Unconformably overlying the Kalkadoon Granodiorite is the Argylla Formation. This is also of Palaeoproterozoic age. It is described as a Felsite (a general term for lavas, clastics and high-level intrusives) and includes porphyritic rhyolitic to dacitic tuff, andesite, quartz feldspar porphyry, quartzite, schist, gneiss; minor siltstone, arkose, conglomerate and metabasalt. The Argylla Formation outcrops on the western margin of both the Wonga and Quamby-Malbon Sub-provinces indicating substantial vertical movement on the Pilgrim Fault that separates the two sub-provinces.
The Marraba Volcanics, a Proterozoic sequence of metabasalt, amphibolite, meta-arenite, schist with minor chert, overlies the Argylla Formation. Unconformably overlying it is the Mitakoodi Quartzite (quartzite, feldspathic quartzite, siltstone, basalt, schist, minor limestone) and the Overhang Jaspillite (jaspilite, limestone, shale, marl). This volcano-sedimentary cycle outcrops as a broad north plunging fold structure which extends from the Pilgrim Fault to Malbon in the east.
The project area is principally underlain by the Corella Formation which is described as a sequence of mixed siliclastic/carbonate rocks comprised of calcareous siltstone, limestone, calcareous scapolitic granofels, quartzite, amphibolite and shale. It is dated as Palaeoproterozoic and is generally regarded as representing a sabka style environment within an intra-cratonic basin. Local accumulations of basic volcanics are present within the Corella Formation as both fine grained lavas with inter-mixed volcaniclastics and medium grained porphyritic high level intrusives. These sediments and volcanics have been regionally metamorphosed to amphibolite facies.
Intruding the Corella Formation in the centre of the project area are the Overlander and Revenue Granites, medium to coarse grained leucogranites of Mesoproterozoic age which have high radiometric counts suggesting that they would have stayed “hot” for long periods of time. They are thus a possible source for fluid and metal ions which may have ponded in structural traps against the Pilgrim Fault.
Of similar age, and occurring to the east of the Overlander Granite is the Mount Philp Breccia; a mafite sequence (lavas, clastics and high-level intrusives) including crystal tuff, agglomerate and lithic tuff, minor calcareous granofels and metabasic remnants. This breccia may relate to the intrusion of a granodiorite as an explosive event over a deeper apothesis of the same batholith. A granodiorite melt is postulated from the strong regional magnetic signature that occurs under the Mount Philip Breccia in contrast to the magnetic lows that correspond with the Overlander and Revenue Granites. Breccia veins of similar texture and compositional style to the Mount Philp Breccia are recorded in the hanging wall and footwall sequences of the Kalman Zone as discordant metre and sub-metre zones.
Structure
The dominant structures within the project area are the Pilgrim and Fountain Range Faults. The Pilgrim Fault extends for over a 100 km from north to south and separates the Wonga and Quamby-Malbon Sub-provinces. Within the project area it is mapped at the junction of the Overhang Jaspillite and the Corella Formation but actually occupies a 500 - 1000 m wide zone and consists of sub-parallel quartz breccia and quartz-manganese veins within variably sheared metamorphics. The Fountain Range Fault is best displayed at Fountain Springs where it consists of a wide (+200 m) quartz breccia vein standing 100 m above the general topography.
The Pilgrim Fault is interpreted as the eastern limb of a north trending wrench fault system that abuts the rigid Kalkadoon block in the west. The Fountain Range Fault, and the other northeast trending structures that parallel it to the south (Overlander, Revenue, St Andrews) are interpreted as Riedel style faults within the north trending wrench fault.
Mineralisation
Copper mineralisation is widely dispersed through the project area. In the north there is some correlation with north-northeast trending quartz shears that are associated with the Pilgrim and Fountain Range Fault Zones.
Gold mineralisation is recorded at Kalman, the Mount Philp gold prospect and at Tick Hill where 706 000 tonnes (t) at an average grade of 22.5 grams per tonne (g/t) gold was mined in the 1990s.
The Mount Philp iron deposit is located at the northern end of the Trafalgar tenement. In 1955 Carter & Brooks estimated a resource of four million tonnes (Mt) at 37% Fe and 39% Si for the exposed portion of the deposit. There are a number of other small haematite deposits in the immediate area.
Uranium was mined at Mary Kathleen (9.5 Mt at 0.13% U3O8) and uranium mineralisation is reported at the Elaine Deposit, both of which occur to the northwest of the Trafalgar tenement. It is also noted as a minor constituent at the White Dingo deposit in the eastern portion of the Trafalgar tenement. Small uranium anomalies are noted in airborne surveys at Corella, Overlander and the Kalman/Pelican line.
In the western portion of the Mount Isa project small scale mining of lime for smelter flux has occurred. Minor copper mineralisation is common within these deposits. These lime deposits are predominant along the western margin of the Corella Formation and may indicate a broad age relationship within the Corella of younging from east to west.
Local Geology
Stratigraphy
The local stratigraphic sequence at Kalman consists of a steeply west dipping hanging wall sequence of meta-volcanics comprised of both fine grained and porphyritic feldspar-hornblende±magnetite rocks; a central (mineralised) zone of feldspar altered meta-sediments; and a footwall zone of chloritic schists and variably textured meta-basic rocks. Extensive shearing has occurred along the Kalman Fault Zone with the most recent event being represented by an unmineralised, multi-staged brecciated/annealed quartz vein which has transgressed the mineralised zone and forms a prominent ridge through the deposit.
Kalman is located in an area of complex structural architecture. Mineralisation is located adjacent to, and near the intersection of a set of sub-parallel 060° trending widely spaced fractures, and two northerly trending brittle-ductile deformation zones that occur within and sub-parallel to the regional-scale Pilgrim Fault Zone. Although the northeast trending fracture sets are possible hydrothermal fluid pathways, and the meta-sediment package a possible receptive host lithology, actual fluid sources and pathways can only be inferred due to the intense metasomatic alteration that has occurred.
At Kalman the mineralised zone is displaced 150 m to the east by a 060° trending dextral fault with a surface trace in the vicinity of drillhole K-02. Mineralisation north of this fault is interpreted to be down-thrown and could extend along strike for a further 800 m, and possibly 1800 m.
Alteration and Mineralisation
Kalman represents an intrusion-related style of hydrothermal Mo-Re-Cu-Au mineralisation hosted by calc-silicate rocks originally comprised dominantly of alkali feldspar with lesser tremolite, apatite, biotite and sphene.
Sodic metasomatism of these calc-silicates, possibly during the early onset of the hydrothermal cell, converted the alkali feldspar to principally albite with actinolite, calcite and chlorite. Fine haematite inclusions within the albite (and lesser potash feldspar) provide the characteristic “red-rock” alteration style.
The poly-metallic mineralised system is outlined by the 300 ppm copper grade boundary in fresh rock. Mineralisation has been traced continuously over a strike length of 1000 m, a depth of 700 m below surface, and consistently averages 80 - 90 m in width. The mineralised zone dips sub-vertical to steeply west, however there are some local steep dip reversals to the east. Step out drilling to the north and south have identified Kalman style geochemical signatures over a strike length of 7 km.
The metal suite is suggestive of oxidised hydrothermal carbonate rich fluids derived from a highly fractionated intrusive felsic source. Chalcopyrite-molybdenite mineralisation is accompanied by a hydrothermal alteration assemblage of calcite-chlorite-minor quartz without the development of intense or pervasive silicification and quartz veining.
Little correlation exists between copper and molybdenum grades suggesting they are probably associated with separate mineralising events. The molybdenum mineralisation occupies the core of the alteration zone and is associated with the most pervasively altered rocks. The copper-gold mineralisation maps the extent of the altered zone and can occur wherever alkali feldspar alteration occurs as well as in association with graphite. The paragenic sequence is yet to be absolutely determined as cross-cutting relationships exist for chalcopyrite over molybdenite and molybdenite over chalcopyrite. Broadly speaking it is believed that the molybdenum mineralisation occurred first and was over-printed by two phases of copper-gold mineralisation.
The mineralisation is believed to be related to two major pulses of CO2 rich fluids followed by a silica rich phase. Pulse 1 introduced molybdenum and uranium mineralisation as disseminations and discontinuous veinlets into the core of the hydrothermal system within the pervasively altered albitites. This mineralisation is interstitial with calcite, chlorite, minor apatite and trace allanite. The restricted development of the uranium-REE mineralisation may vector fluid pathways.
Pulse 2 introduced chalcopyrite±pyrite±gold over the width of the alteration system. Copper mineralisation occurs throughout the pervasively altered core as well as within fracture controlled veins of albite and K-feldspar alteration around the margins. Chalcopyrite and pyrite also feature in the partially altered banded metasediments, especially in the coarser grained bands and within graphitic zones. Chalcopyrite is also noted in some of the tri-modal breccia veins.
Pulse 3 is represented by narrow quartz±calcite veins containing chalcopyrite±pyrite which transgress the other mineralisation styles. This style of mineralisation can be significant as represented by one drillhole intersection of 7.65 m grading 23.4% Cu, 0.5 g/t Au, 19.8 g/t silver (Ag) (Hole K-106A; 581.65 m to 589.30 m).
The mineralisation generally occurs as fine grained disseminations and anastomosing discontinuous millimetre-wide veinlets of chalcopyrite and molybdenite. Pyrite averages <1% even in the most richly mineralised areas. Rhenium is present in significant amounts as inclusions within the molybdenite lattice; uranium occurs as discrete uraninite and covellite grains only within the molybdenum rich areas; minor bornite and chalcocite mineralisation occur as regressive phases generally along grain boundaries; and although the gold and copper grades appear correlated the gold is thought to be held within the associated pyrite grains.
Post mineralisation retrogressive hydrothermal alteration is evident with the partial to complete replacement of diopside, albite and potash feldspar with sericite and/or calcite; biotite and actinolite with chlorite; and rutile and sphene with leucoxene. Extensive post mineralisation shearing and quartz veining is evident; this has been accompanied by the development of graphite. Fine calcite veins ±epidote±haematite represents the last vestiges of the hydrothermal cell. Fluorite occurs in some late stage calcite veins cutting Cu-Mo mineralised host rocks.
The polymetallic mineralised system is outlined by the 300 ppm Cu grade boundary in fresh rock. Mineralisation has been traced continuously over a strike length of 1,000 m, a depth of 700 m below surface, and consistently averages 80 to 90 m in width. The mineralised zone dips sub-vertical to steeply west however there are some local steep dip reversals to the east. The metal suite is suggestive of oxidised hydrothermal carbonate rich fluids derived from a highly fractionated intrusive felsic source.
The Kalman alteration-mineralisation system has a “hyperspectral signature” of white mica coincident with the Cu-Mo-Au mineralisation which is continuous over a strike length of 1 km. The composition of this white mica changes along strike with Al-poor mica (phengite) found coincident with mineralisation. Several similar “hyperspectral anomalies” are recognised in the area of which the most significant is Pelican, 3 km south of Kalman. The Pelican prospect is also located in an area of complex structural architecture adjacent to the Pilgrim Fault with overlapping anomalous soil copper geochemistry, other anomalous hyperspectral responses plus historic copper workings.
