Malmsbury
Victoria has been a gold producing region since the first documented discovery of gold at Clunes, located 50km west southwest of Malmsbury, in July 1850. The announcement stimulated prospecting in the district and on 20 July 1851 gold was found at the foot of Mt Alexander, only 20km north-west of Malmsbury. This became the richest alluvial gold field the world had ever seen, with 3.5 million ounces of gold dispatched to Melbourne in a ten year period from a creek length less than 3km long.
A few months after the Mt Alexander discovery, the Bendigo goldfield was found and produced over 22 million ounces of gold. Victoria has been a significant gold producing region for over 150 years.
Targeting Intrusion Related Gold Deposits
Generally, gold deposits in central Victoria are classified as orogenic gold style deposits which are typically characterised by gold collecting as irregular and unevenly dispersed small nuggets that are usually contained in veins of quartz within the host rock.
The target geological structures in the Company’s Victorian project areas are the economically important class of deposit commonly called intrusion related gold deposits. Such deposits are generally characterised by more evenly disseminated gold mineralisation at appreciable grades that may also display a high degree of continuity. These characteristics can assist in the economic extraction of ore.
Malmsbury Project – EL 4515 & EL 5120
The Malmsbury project comprises of two tenements, EL 4515 (which includes the amalgamation of EL 4503) and covers an area of 22.0 square kilometres.
And the recently granted, Exploration Licence EL5120 which was applied for soon after listing in 2007 to cover possible extensions to the Malmsbury Project - Drummond North Goldfield, and also allow investigation of several other areas of gold mineralization located by reviewing historical records of the geological Survey of Victoria.
This licence provides a strategic ground holding allowing GBZ to explore the area on a system based approach.
The area includes numerous historic gold occurrences on which considerable work has been conducted using traditional Victorian reef gold models to direct the exploration. Initial prospecting in EL 4503 identified over 30 historic gold pits and underground mine workings.
The first gold in the Malmsbury district was also discovered in 1851 near Lauriston and was followed in 1852 by discoveries at Taradale. In 1856 there were discoveries of rich auriferous deep leads and quartz reefs.
The Drummond North goldfield located in the northern area of the Malmsbury project produced 98,000 tonnes of ore at an average grade of 29 g/t Au, or approximately 91,000 ounces of gold, in the late 19th century. The main producing mines were the Queen's Birthday (39k ozs) and O'Connors Freehold (39k ozs).There is no record of work done in the area from 1916 to 1964 and since then there has been little targeted exploration activity or drilling.
Within the Malmsbury project area the main prospects are disseminated shear related deposits in the vicinity of Belltopper Hill. The historic mines at Belltopper Hill were centred on three reef structures namely Leven Star, Missing Link and Panama reefs.
Two types of mineralisation have been investigated to date at Belltopper Hill, one comprising of steeply dipping, north trending quartz reefs or strike reefs at Panama and Missing Link that were worked to shallow depths in the late 1800s, the other is the north east striking reef that was worked for a short time in the 1930s as Andrew’s lode but more recently as Leven Star reef.
High resolution imaging of airborne geophysical data from the Belltopper Hill area indicates two small circular features underneath and to the west of Belltopper Hill that could be subsurface igneous bodies. This is supported by the distinctive photo lineament pattern in the vicinity of Belltopper Hill.
The target deposit style within the Malmsbury project are intrusion related gold deposits. Deposits of this type elsewhere in the world include world class gold ore bodies such as:
The area includes numerous historic gold occurrences on which considerable work has been conducted using traditional Victorian reef gold models to direct the exploration. Initial prospecting in EL 4503 identified over 30 historic gold pits and underground mine workings.
The first gold in the Malmsbury district was also discovered in 1851 near Lauriston and was followed in 1852 by discoveries at Taradale. In 1856 there were discoveries of rich auriferous deep leads and quartz reefs.
The Drummond North goldfield located in the northern area of the Malmsbury project produced 98,000 tonnes of ore at an average grade of 29 g/t Au, or approximately 91,000 ounces of gold, in the late 19th century. The main producing mines were the Queen's Birthday (39k ozs) and O'Connors Freehold (39k ozs).There is no record of work done in the area from 1916 to 1964 and since then there has been little targeted exploration activity or drilling.
Within the Malmsbury project area the main prospects are disseminated shear related deposits in the vicinity of Belltopper Hill. The historic mines at Belltopper Hill were centred on three reef structures namely Leven Star, Missing Link and Panama reefs.
Two types of mineralisation have been investigated to date at Belltopper Hill, one comprising of steeply dipping, north trending quartz reefs or strike reefs at Panama and Missing Link that were worked to shallow depths in the late 1800s, the other is the north east striking reef that was worked for a short time in the 1930s as Andrew’s lode but more recently as Leven Star reef.
High resolution imaging of airborne geophysical data from the Belltopper Hill area indicates two small circular features underneath and to the west of Belltopper Hill that could be subsurface igneous bodies. This is supported by the distinctive photo lineament pattern in the vicinity of Belltopper Hill.
The target deposit style within the Malmsbury project are intrusion related gold deposits. Deposits of this type elsewhere in the world include world class gold ore bodies such as:
- Cadia Ridgeway gold mine in New South Wales that has in excess of 20m ounces of contained gold in resource;
- Kidston gold mine in Queensland that operated between 1985 and 2001 and produced over 3.5 million ounces of gold;
- Fort Knox gold mine in Alaska that currently produces over 400,000 ounces of gold annually; and
- Pogo gold mine also in Alaska that holds an estimated resource of 5.6
million ounces of gold.
Leven Star Prospect
Unlike the nearby Panama and Missing Link strike reefs, the Leven Star reef has a distinctive gold-sulphide association and sulphide-carbonate alteration that are often indicative of hydrothermal systems that have an interpreted relationship to intrusive related gold deposits.
The Leven Star reef follows a brittle mineralised fault zone with associated intense fracturing and subparrallel quartz veining in country rock up to 30m wide. Exploration drilling in the early 1990s defined a 450 metre long zone of gold mineralisation. Results from previous drilling included the following:
| Intercept Metres | Grade g/t AU |
| 1.0 | 33.2 |
| 4.1 | 13.1 |
| 6.6 | 8.2 |
| 8.6 | 5.66 |
| 5.0 | 5.39 |
| 6.3 | 5.02 |
| 11.0 | 4.6 |
| 16.0 | 3.78 |
| 10.0 | 3.63 |
| 7.7 | 3.25 |
| 14.0 | 2.80 |
| 14.0 | 2.59 |
| 30.0 | 2.16 |
The 6 hole diamond drilling programs that targeted the Leven Star Zone prospect last year, part of the Malmsbury Project in Central Victoria, has resulted in the inferred resource increasing to 0.8 Mt at an average grade of 4.0 g/t Au containing 104,000 ounces of gold using a 2.5 g/t Au cut off grade (see table 1).
The increase is largely attributable to extending the resource model to depth based on information from GBZ’s diamond drilling programme completed during 2008. The resource is considered open both to depth and along strike. Details of the parameters used are contained in the resource statement which can be accessed on the company’s website.
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Cut-off : 2.5 g/t Au
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Resource Classification
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Tonnes (x103)
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Au (g/t)
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Au (x103 ounces)
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Inferred
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820
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4.0
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104
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Note. Cutoff grade reflect anticipated underground mining production costs.
Table 1: 2008 Leven Star Gold Resource Estimate
High grade results from rock chip samples collected during the December quarter are summarised on figure below and support higher grades intersected in drilling of the southern portion of the Leven Star Resource. Samples returned values up to 24.9 g/t Au in variably sheared and altered sediment host rock with quartz vein stockwork development.
Some 80 samples from GBM’s 2008 diamond drilling programme at Leven Star and Queen’s Birthday were submitted to a second independent laboratory for repeat analyses. The results showed a very strong correlation (correlation co-efficient 0.9). One of two significant outliers corresponded to a sample from the Queen’s Birthday mineralised zone in MD11. The initial result of 0.9 g/t Au corresponded to a value of 5.2 g/t Au. This is suggestive of a small component of coarse gold and is being checked with fire assay; however the strong correlation in the overall data set indicates that this is uncommon in the Drummond North Goldfield.
Resource Potential of the Malmsbury Project-emerging as a major gold system
Review of available historical and recent exploration and mining data conducted by GBZ staff during 2008 has confirmed a known gold endowment of 195,000 ounces of gold in the near surface (approximately 150 metres from surface) portion of the structurally controlled mineralized zones explored or mined to date. This endowment comprises 91,000 ounces of historical production and 104,000 ounces of the current Leven Star Resource. At this time production from a number of shafts in the project area are still unknown, and many zones remain to be drill tested and resources evaluated. In addition the Drummond North Goldfield remains open along strike both to the North and to the South. The current estimate of gold endowment is considered incomplete in the near surface environment
The Drummond North Goldfield remains open at depth. Numerous goldfields exist within the prolific gold producing region of Central Victoria. In many cases mining and resources extend to depths well in excess of one kilometre, or more than seven times the depth which contains the .02M ounce gold endowment confirmed to date at Drummond North. The Stawell Gold Mine is currently extracting ore from underground operations some 1200 metres below surface and planning to develop to greater depth. Previously reported drill hole MD8A intersected gold mineralisation in the Leven Star Zone at approximately 300 metres below surface confirming that mineralisation extends well below the known resources.
GBZ believe that the Malmsbury Project is emerging as a major gold system in a world class gold province. Modern exploration is now revealing deposits that were difficult for prospectors to discover or exploit in the past, including Northgate’s Fosterville Gold Deposits which now have a known gold endowment of 4Mozs and growing as exploration continues to define further resources.
Rediscover Victoria Grant to further test potential for Large Gold Tonnage (IRGD).
GBZ has been successful in it’s application for a grant through the Rediscover Victoria Drilling Initiative to test the gold mineralising system in the Malmsbury Gold Project - Drummond North area at depth with a deep (approximately 1 kilometre) drillhole. A large tonnage IRGD remains the long term target for GBZ in the Malmsbury Project area. The Drummond North Goldfield includes a number of structurally controlled mineralized zones (Leven Star, Queen’s Birthday, O’Conners, Missing link etc.) which while significant in their own right, may be proximal to a major IRGD. Previous mineralogical and alteration studies have recorded features indicative of an intrusive related gold systems (IRG). Petrographic and geochemical data collected during the 2008 drilling are interpreted to further support this conclusion. IRDG deposits include a number of +3Moz deposits and continue to represent an attractive exploration target style for GBZ.
Malmsbury Project - Leven Star Deposit 2008 Resource Statement and Estimation Methology