Rockfire’s Marengo Gold/Copper/Silver Project is a structurally-controlled, high-level Intrusion Related Gold System (IRGS) incorporating the entire historical Marengo Goldfield. Located in central Queensland and lying within a high-density belt of porphyry copper deposits, Marengo provides Rockfire opportunity to discover high-grade gold and large-scale porphyry copper deposits with silver credits.
Gold was first discovered at Marengo in the late 1870’s and hosts thirty-seven (37) historical gold diggings. Hand-picked production is recorded as averaging 2oz/t Au (62g/t Au). During the height of its mining days, more than 200 people lived at Marengo working the many diggings and shafts in the area.
In 1921, the area was being explored by individuals and a record by a Mr. Moreton noted that all the small gullies were said to carry gold and that one of his hard rock samples contained 29 dwts per ton (46.5g/t Au).
During 1935, whilst prospecting in the area, a Mr. Ridgeway noted that rock sampling of a large hill of quartz (now known as Westwood Hill) returned an average grade of 10 dwts per ton (15.5g/t Au).
Throughout the tenement and particularly in the proximity of One Mile Mountain, strongly anomalous geochemistry has been detected with rock samples up to 17g/t Au, 2.16% Cu and 78g/t Ag.
Costeaning has returned 12m @ 6.10g/t Au and thirty-nine (39) drill holes have been drilled by previous explorers. Significantly, twenty-nine (29) of these holes are vertical, making this drilling ineffective as vertical holes are not considered appropriate as all known mineralised veins are vertical or steeply dipping. The better results from this drilling ranged between 0.62g/t and 1.13g/t Au.
Marengo is related to numerous, parallel, north west/south east trending faults which intersect a zone of north/south trending fault zones. The intersection of these faults creates a highly fractured and rotated structural environment resulting in increased fluid percolation. Mineralisation is precipitated in high-grade zones focussed within and proximal to the intersection points.
Marengo is vastly under-explored. Although numerous copper and gold occurrences are mapped and the tenement contains abundant structural targets, there has been limited focussed exploration work completed within the Rockfire tenement area.
Potential exists to identify structurally-controlled, intrusion-related copper and gold deposits occurring at the margins of the monzonites and granites mapped within the tenement. The margins of a large regional gravity low covered by the Marengo licence provides an outstanding target for high-grade vein and breccia-hosted deposits originating from the interaction of this vast intrusive complex with the surrounding rocks.
The multiple events producing rock variations between granite through to gabbro is testimony to the multi-phase episodes which are favoured precipitation settings for precious and base metals. These multiphase intrusions require detailed mapping and sampling to
The first company to take out a lease which covered the Marengo Goldfield was St Joseph Phelps Dodge in 1968. Phelps collected 2200 stream sediment samples throughout the region and completed initial geological mapping. They concluded that a very flat geochemical signature dominated the entire area with the highest sample returning 60ppb Au from the Marengo Goldfield area itself.
Carpentaria Gold, Central Coast Exploration, Esso Exploration and AOG Minerals all acquired brief tenure over the broader region between 1970 and 1980 but none of these companies completed any significant exploration work.
The first serious work programs were put together by Intek Services when they acquired the tenement in 1981. Intek undertook rock chip sampling of the individual reefs, as well as semi-regional stream sediment sampling which focused on One Mile Mountain and the Three Brothers areas. This work was extremely successful with most rock samples ranging from 2.0g/t Au – 17.4g/t Au. Intek suggested that around One Mile Mountain, “maximum reserves indicated were approximately 100,000 tonnes of 6g/t Au and significant Ag values”. The company went on to state that “the One Mile Mountain structure could be of possible economic importance”.
In 1987, Xenolith Gold acquired the tenement and undertook initial rock sampling which identified high grade gold and silver at the workings including;
- Flat Reef – average assays of 5.4g/t Au and 50.2g/t Ag
- Westwood – average assays of 2.1g/t Au and 9.0g/t Ag
- Homeward Bound – assay range from 0.3g/t – 6.7g/t Au and 1.0g/t – 92g/t Ag.
- Manchester Reef – assays range from 0.02g/t – 60g/t Au and 4.0g/t – 100g/t Ag.
Of interest is the lack of copper analysis by Xenolith, given that the rocks are described as “copper-stained gossanous material”.
Xenolith continued its exploration in 1988 by drilling 39 RC drill holes. These holes were drilled at the following locations;
- Homeward Bound – 5 holes (PD1 – PD5).
- Toomeys – 4 holes (PD6, 7, 8, 8A).
- Westward – 8 holes (PD9 – PD16).
- Flat Reef – 22 holes (PD17 – PD39).
The better results from this drilling ranged between 0.62g/t and 1.13g/t Au. Many of the holes terminated prematurely due to caving, water and shafts/adits. Most of the holes were drilled vertical which is not considered appropriate in an epithermal/structural/fault-hosted setting. The drilling recoveries were very poor (down to 6%) and full recovery using modern drilling equipment is expected to increase gold values materially.
Fawdon & Skett held the tenement centred on One Mile Mountain during 1993. Exploration work resulted in “…the delineation of several anomalous zones for gold, silver and copper, with the main area of anomaly centred on a zone 2000m in length traversing the southern slope of the One Mile Mountain Porphyry Gold Deposit”.
On the western and southwestern flanks of One Mile Mountain, rock values up to 30.4g/t Au, 215g/t Ag and 3.15% Cu were identified. At Westwood Reef (to the south of One Mile Mountain), very high-grade gold, silver and copper (up to 20.7g/t Au, 89g/t Ag and 1.38% Cu) were also encountered. Quartz veins extending outwards from One Mile Mountain towards the east returned high-grade assay results including the highest grade achieved of 149.8g/t Au.
In 1994, Strike Exploration acquired the tenement covering the goldfield and completed geological mapping and collected 67 rock chip samples. A further 28 samples of clay/loam/sand were collected for dollying on site. These samples presented numerous colours in panned concentrates.
Finally, in 1997 Australian Oriental Minerals applied for the licence over Marengo, which was finally granted in 2007. Between 2007 and 2012, Australian Oriental Minerals did not undertake any field work and all work was confined to desk top studies and literature reviews.
No field work has been completed in the Marengo area since 1994.
Geological map of the One Mile Mountain area
Quartz outcrop at Homeward Bound
One Mile Mountain is considered a high priority by Rockfire and incorporates multiple historical mines within an area of approximately 2km2. The workings at One Mile Mountain include Albion, Three Ways, Westwood, Flat Reef, Homeward Bound, Toomey’s, Frankie’s, Sulphide Shaft and Hill Top.
The Albion historical mines contain high-grade gold in rock samples including 18.7g/t Au, 30.4g/t Au and 7.5g/t Au. Albion is situated on east-west trending structures within an altered diorite. No historical costeaning or drilling has been completed at Albion. Albion is located proximal to intersection zones between north-west and east-west trending faults, magnetite alteration zones, and quartz veining. Albion is considered a high priority target.
The Three Ways historical mines contain high-grade gold in rock samples (e.g., 6.9g/t Au, 10.0g/t Au and 7.0g/t Au), as well as 149.80g/t Au which represents the highest value obtained to date from the Marengo Project. Three Ways is situated on east-west trending structures within an altered diorite and hosts an Aplite dyke and north-west trending quartz veins. Owing to the extremely high-grade rock samples, its proximity to intersecting east-west and north-west trending faults and subsequent intrusion/alteration, the Three Ways Prospect is considered a high-priority target.
The Westwood historical mines contain high-grade gold in rock samples, with results including 11.8g/t Au, 20.7g/t Au, 17.0g/t Au, 15.0g/t Au and 11.0g/t Au. Eight open hole percussion RC drill holes were completed in 1989 by Xenolith at Westwood. Each hole (PD09 to PD16) was drilled vertical and only sampled sporadically. From a total of 150m drilled, only 26m were assayed. Westwood is located in an altered diorite with east-west trending structures and quartz veining. Westwood is considered a high-priority target because of the presence of altered diorite, high levels of structural faulting and high-grade rock samples.
The Flat Reef historical mines contain high-grade gold in rock samples (e.g., 16.2g/t Au, 50.0g/t Au 18.4g/t Au, 12.8g/t Au and 10.4g/t Au). Costeaning was completed in 1988, however there is no mention in the literature of the length of each costean, the length of each individual costean sample, type of costean sample collected, nor a map clearly identifying the location of each costean. From assumed individual sample lengths of 1m, costeaning returned an interval of 12m @ 6.06g/t Au. Twenty-two (22) open hole percussion RC drill holes (PD17 – PD22, & PD 24 – PD39) were completed in 1989. Each hole (PD09 to PD16) was drilled vertically and sparsely sampled (of 487m drilled, only 127m were actually assayed). The drill logs report very low sample recoveries down to as little as 6%. This prospect is considered to be a high priority target due to the poor recoveries and the high-grade rock and costean samples.
Homeward Bound contains high-grade gold in rock samples of 23.5g/t Au, 6.7g/t Au and 8.4g/t Au. Five (5) open hole percussion RC drill holes were completed in 1989 by Xenolith at Homeward Bound. Each hole (PD01 to PD05) was only sporadically sampled (of 200m drilled, only 26m were submitted for analysis). The drill logs report very low sample recoveries down to as little as 30%.
The Toomey’s mines contain high-grade gold in rock samples including 4.4g/t Au and 1.4g/t Au. Four (4) open hole percussion RC drill holes were completed in 1989. Each hole (PD06 to PD08a) was only sporadically sampled (of 141m drilled, only 12m were actually analysed). The drill logs report very low sample recoveries down to as little as 45%.
The New Reef was discovered by regional geochemical sampling of historical workings which were not recorded in the old literature. Rock sampling (25g/t Au) and costeaning at New Reef during 1988 proved very encouraging. There is no mention in the literature of the length of each costean, the length of each individual costean sample, type of costean sample collected, nor a map clearly identifying the location of each costean. From assumed individual sample lengths of 1m, Costean 1 intersected 12m @ 0.91g/t Au, Costean 2 encountered 10m @ 1.22 g/t Au and Costean 3 returned 9m @ 1.03g/t Au. New Reef provides an excellent exploration target for further work.
The Bee Hill workings are situated in the western part of the Marengo Tenement. Surface rock samples returned high-grade gold of 7.1g/t Au, 4.0g/t Au, and 2.3g/t Au. Bee Hill is located in a zone of north-west trending faults. No drilling or costeaning has been completed at the Bee Hill prospect, which is considered a medium level target.
The Bee Creek workings are situated in the western part of the Marengo Tenement (south-east of Bee Hill). Historical rock samples returned high-grade gold including 29.9g/t Au, 10.7g/t Au, 11.1g/t Au, 3.3g/t Au, 4.4g/t Au, 8.2g/t Au and 22.4g/t Au. Bee Creek is located in a zone of north-west trending faults. Should Bee Hill and Bee Creek Prospects prove to form a single, cohesive mineralised system, then this would result in a mineralised corridor in excess of 5km strike. No drilling or costeaning has been completed at Bee Creek.
The 300-Ounce Patch historical workings are situated in the central part of the Marengo Tenement. Surface rock samples have returned high-grade gold results which include 5.0g/t Au, 11.8g/t Au, 4.0g/t Au, 18.9g/t Au and 18.0g/t Au. No drilling or costeaning has been completed at 300-Ounce Patch.
Three additional historical mines returned high-grade gold in rock samples; Frankie’s (16.6g/t Au), Sulphide Shaft (14.0g/t Au, 8.6g/t Au) and Hill top (17.4g/t Au, 25.2g/t Au and 5.5g/t Au). No drilling or costeaning has been completed at any of these prospects. They each occur in metasediments proximal to the intersection of east-west and north-west trending faults and provide opportunity for new discoveries for Rockfire.
Regional targets identified from stream sediment sampling
Three hundred and thirty-nine (339) stream sediment samples, comprised of data sourced from nine different companies have been combined into a single database by PML. This compilation has revealed 10 significant anomalies which require follow up exploration work.