Mount Isa
‘Mount Isa – nothing else on earth measures up’
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Introduction: Mount Isa Region
GBM identified the Mount Isa Inlier as fitting with its strategy of seeking world class copper–gold deposits in world class mineral provinces and was designated a priority area. During the second half of the year the company acquired ten tenements in the Eastern Fold Belt of the Mount Isa Region from Newcrest Mining Limited. This is a strategic holding in a world class mineral province which represents a substantial increase in the value and prospectivity of the company’s portfolio of mineral exploration tenements.
The Proterozoic Mount Isa Block is recognised as one of the most fertile provinces on earth for the discovery of metallic mineral deposits. The concentration of world class deposits is unrivalled; nothing else on earth measures up. The Mount Isa Inlier contains four of the world’s ten largest zinc deposits, three of the ten largest lead deposits and three of the ten largest silver deposits. There are also numerous copper deposits with twenty four deposits each containing over 400,000 tonnes of copper including (three deposits that contain over 1 million tonnes of copper) and fifteen deposits are hosted by the Eastern Fold Belt. Most of these deposits (and all of those hosted in the Eastern Fold Belt) contain economically significant levels of associated gold mineralisation. (Queensland Department of Minerals and Energy, Taylor Wall & Associates, SRK Consulting Pty Ltd & ESRI Australia, 2000: North West Queensland Mineral Province Report. Queensland Department of Minerals and Energy, Brisbane. Queensland Minerals, a Summary of Major Mineral Resources, Mines and Projects, Fourth Edition. Queensland Department of Minerals and Energy, Brisbane)
Despite the fertility of the region, the last major new discovery was Ernest Henry in 1991. With the slow down in mineral exploration through the 1990’s and early part of the new millennium, many areas have not been actively explored for almost two decades. In this time significant advances in understanding of ore deposit styles and in exploration techniques have occurred. GBM will harness these advances, particularly in the application of electrical geophysical techniques in areas of cover, to further exploration of our tenements.
The most common deposit style is Iron-Oxide-Cu-Au (IOCG), a deposit style which includes many very large deposits throughout the world, including the massive Olympic Dam Cu-Au-U Deposit in South Australia; however other styles including sediment hosted mineralisation are also represented in the region. In addition the area contains a number of Uranium occurrences.
The emergence of the overlying Georgina Basin sediments as one of the world’s major phosphate provinces with phosphate resources currently identified totalling over three billion tonnes also highlights the potential of the area.
Talawanta- Grassy Bore Project (EPM15406 & EPM15681)
Talawanta and Grassy bore licence areas are centred on a north trending linear magnetic complex interpreted to represent a feature in the underlying Proterozoic basement (extension of Mount Isa Inlier under cover). The magnetic complex is locally extremely intense, particularly given the depth of the cover sequence which would tend to mask the magnetic response. Previous drilling has confirmed the presence of widespread copper mineralisation and associated hydrothermal alteration. This region is outside the outcropping Mount Isa Inlier under the Carpentaria Basin cover sequence, in this area reported to be 300 to 500m thick.
Talawanta is centred on a major magnetic anomaly which is the most intense anomaly in the district next to Ernest Henry. The magnetic anomaly is 15km x 7km in area. The anomaly has been drill tested by three drill holes which intersected alteration and zones of Cu–Au mineralisation.
The magnetic anomaly is clearly associated with alteration and the potential for discovering IOCG style mineralisation is considered high.
Grassy Bore is centred on a series of bulls eye magnetic and gravity features. Limited drilling has confirmed the presence of alteration and weak mineralisation. The depth of cover is reported as around 300 metres. Grassy bore also contains valid targets for IOCG style mineralisation.
Talawanta & Grassy Bore Tenement areas over back drop of TMI image displaying very strong magnetic highs which are considered targets fo IOCG style mineralisation
Mount Margaret Project (EPM1627, EPM14614, EPMA 16398 & EPMA16222)
These tenements are situated in the same geophysical and geological domain as the Ernest Henry Cu-Au Mine currently operated by Xstrata Plc.
The tenements are centred on a series of magnetic anomalies that surround prospective granites. The area also contains extensive geochemical targets (Cu, Au), though the relationship with basement magnetic features has not been established in our review to date. It is a highly mineralised district with Ernest Henry and Mt Margaret deposits located nearby.
Brightlands Project (EPM14416)
The Brightlands tenement area is located south east of Cloncurry on the Barkly Highway. Previous exploration by several companies had generally been narrowly focused and had not evaluated the area with a view to understanding the geological system. The result is that numerous prospects have been defined but with limited geological understanding apparent of their potential size and relationships to each other. Previous exploration has been focused on individual commodities. Explorers that targeted copper, for example, seldom analyse for gold, and Uranium explorers appear not to have tested for copper and gold. Most drilling was completed over thirty years ago with limited geological control evident from our initial review. The area contains the Milo Uranium occurrence which has a recorded production of a minor quantity U3O8.
Widespread mineral occurrences are considered to hold potential for IOCG and high grade Tick Hill (Au) styles of mineralisation. Multiple exploration target areas have been identified by previous explorers, however initial examination indicates that the following are of high priority for immediate follow-up;
- Milo & Milo West Prospects- multiple zones of gossan and Cu bearing
shears (and breccias) hosted by Dolerite overlain by Calc-silicate.
Surface rockchip samples frequently returning >1% Cu and 0.3ppm Au,
limited drilling indicating significant sections of >0.1% Cu with no Au
assays. The old Milo Mine was noted as a Cu-U occurrence
· Fine Gold Gully- interpreted by Newcrest as being in a similar stratigraphic position as the Tick Hill Mine (470,000t @ 28g/t Au) with a similar geochemical anomaly, one hole drilled over weaker (30ppb in soil) geochemical response returned 6m @ 0.2g/t Au and 0.23%Cu.
· Tiger Prospect- anomalous gold in rock chip samples in shear zone interpreted as part of a structural zone hosting the Rocklands deposit (Cudeco) located 3km northwest. Rock chip sampling of the structure has returned Au values up to 1.87g/t Au and copper values up to 17%. The Rockland’s mineralisation is relatively narrow at surface or has no surface expression in places, however at depth it turns into a 20-30m wide mineralised structure.
· Prospects with anomalous Cu, Au, Zn and Mn are associated with the extensive Chumvale Breccia Unit.
Brightlands tenement over TMI image of the region. Brightlands contain multiple targets fro Au and Cu-Au-U mineralisation
Bungalien - Horse Creek Project (EPM14355, EPM15150 & EPM14120)
These tenements are centred on a series of geophysical targets (magnetic highs) which are overlain by Georgina Basin Sediments. The magnetic highs are interpreted as potentially representing Iron Oxide Copper Gold mineralising systems. Recent upward movement in fertiliser prices has greatly enhanced the value of Phosphate minerals as exploration targets. The Cambrian Georgina Basin cover sequence in the area has potential to host phosphate deposits similar to the Phosphate Hill Mine located some 70 km south of the Bungalien tenement. Previous drilling by Newmont in the 1970’s (part of a uranium exploration programme) intersected phosphatic sediments in the Bungalien tenement area, however no analyses were completed.
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The Georgina Basin in Queensland (and Northern Territory) is emerging as a world class Phosphate Province. Key known resources highlighted along with the location of GBM's tenements
GBM's Bungalien and Horse Creek Tenement areas shown over an image created from total count radiometric data