Core Shack › Cobalt Ridge (Mt Gilmore Project)
Cobalt Ridge (Mt Gilmore Project)
Granite related polymetallic veins
Cobalt with a cobalt mineral of its own, and an arsenic partner that tells you where to look.
Drillhole viewer
Every hole GSNSW holds within 750 m of the deposit centre. Drag to orbit, scroll to zoom, tap a collar for its details. Names are masked.
Collars on a local grid in metres from the deposit centre. Traces are drawn vertical. Hole orientation is not published for this deposit.
Veins off a granite, in the Clarence River country
Cobalt Ridge is part of the Mt Gilmore Project near Copmanhurst, north west of Grafton, in the northern New England Orogen. GSNSW classes it as granite related polymetallic veins with a granite genesis. Metal bearing fluid left a crystallising intrusion, found open structures in the rock above it, and filled them.
The mineralisation style is logged as breccia fill and vein. That is the geometry to hold in your head at the tray. Not a layer, not a lens, but cracks and shattered zones that were cemented with sulphide and quartz while the fluid was moving.
Cobaltite, and the arsenic that comes with it
GSNSW lists cobaltite in the ore mineralogy. Cobaltite is a cobalt arsenic sulphide, CoAsS, silver white to steel grey, metallic, and heavy in the hand. It sits with arsenopyrite, chalcopyrite, pyrite and pyrrhotite, with gold as an accessory.
Because the cobalt mineral carries arsenic in its formula, and because arsenopyrite is in the same assemblage, the two elements travel together here. Arsenic is not a nuisance at Cobalt Ridge, it is a pathfinder. The two competition categories on this tray are cobalt and arsenic, and a guess at one should inform the other.
The gangue is tourmaline with quartz, and the alteration is sericitic. Tourmaline is a boron mineral, and boron in a vein selvage next to a granite is the fluid signing its name, the same way it does at Taronga.
Three campaigns, three targets
The drilling around Cobalt Ridge comes in three pulses, and the programs carry different names. The 1983 and 1984 holes belong to the Clarence River and Pulganbar programs. A second pulse in 2006 to 2008 returned to Pulganbar and put diamond core into the ground, and that core is what GSNSW holds in the library.
Then the Mt Gilmore Project, 2016 to 2018, and the busiest decade in the record. RC dominates, which is the method you use when you already know where the structure is and want to test it quickly and often. Colour the collars by era in the viewer and the three campaigns separate cleanly.
What this kind of deposit looks like
An idealised model of the deposit type, built from the GSNSW description. Shape, structure, mineralisation style and alteration. Drag it around.
What to look for in the tray
- Cobaltite: silver white to steel grey, metallic, dense. Look for it with the arsenopyrite, which is paler and often prismatic.
- Breccia and vein textures. Angular fragments in a sulphide and quartz matrix, and the vein walls.
- Tourmaline in the gangue, black and needle like, with sericite bleaching the host next to the veins.
Grade guessing competition
Have a crack at the Cobalt Ridge (Mt Gilmore Project) tray
Running across both days at the Geological Survey of NSW booth, booths 20 and 21, Exhibit Room B.
- Look at the core. Prospect and deposit type are on the card; hole ID and assays are not, on purpose.
- Write your estimate on an entry slip at the booth. There is a category per commodity. For this tray the categories are Co and As.
- Entries are open day 1 and day 2.
- GSNSW hold the assays until the prize presentation on day 2. A bottle of wine per category, supplied by the conference committee.
The GSNSW record
Straight from the Geological Survey of NSW mineral occurrence database, reproduced as supplied.
- District
- not assigned
- Deposit size
- Occurrence
- Major commodities
- Co, Cu, Au
- Ore mineralogy
- arsenopyrite, chalcopyrite, cobaltite, pyrite, pyrrhotite (gold)
- Gangue
- tourmaline (quartz)
- Alteration
- sericitic
- Mineralisation style
- breccia fill, vein
- Deposit class (NSW)
- Granite-related polymetallic veins
- Deposit genesis (NSW)
- Granite
When it was drilled
What is on this page, and what is not. Drillhole names are masked and shown as sequential identifiers. There are no assay results here, and no map coordinates. Collar positions are plotted on a local grid in metres from the deposit centre, rounded to 5 m. That is deliberate: the competition only works if nobody can look up the answer from their phone while standing at the tray.
Everything else, deposit type, commodity, mineralogy, alteration, drilling history, is open file information published by the Geological Survey of NSW.
Source: Geological Survey of NSW (MinView), supplied 2 September 2026. Reproduced with permission. MetaGeo sponsors the Core Shack at Mines and Wines 2026.