Purcell Basin Copper Beds | Learning Centre

Stage 01

1.5 Billion Years Ago (Aldridge Formation)

As the ancient supercontinent of Nuna breaks apart, a rift forms and splits ancestral North America from what will become Siberia and Australia. The rift forms a depression that becomes the Purcell Basin, infilled with a deep sea. The sediments interact with volcanism from the rifting and form deposits such as the Sullivan Mine hosted in the Aldridge Formation.

Stage 02

1.45 Billion Years Ago (Creston-Revett)

The Purcell Basin becomes shallower and starts to infill with sediments eroding from the surrounding highlands in the forms of large deltas. The water is prone to evaporation under an extreme climate, creating hyper-saline brines that get trapped in the sediments.

Stage 03

1.42 Billion Years Ago (Nicol Creek Formation)

A second phase of rifting occurs, and the crust is uplifted, displacing the seawater in the Purcell Basin. Basaltic lava floods over the exposed seabed, trapping the saline brines in the underlaying layers. The basalt is also rich in copper, iron and other metals which will play a role in the fertility of the Purcell Basin.

Stage 04

1.4 Billion Years Ago (Sheppard Formation)

As the volcanism ceases, the crust deflates, and the waters return to the basin forming a broad but very shallow sea. These form ideal conditions for reefs made of mounds of cyanobacteria called “stromatolites” which we find fossilized across the project site. Unlike the older layers of sand and silt, the Sheppard Formation is dominated by carbonates and dolomitic rocks.

Stage 05

840 Million Years Ago

Over half a billion years pass and more sediments build up in the basin creating immense pressures. The brines trapped between grains start to circulate as they are squeezed, and their caustic nature dissolves metals from the rocks and transports them to focused traps. Some access the polymetallic Aldridge Formation, while others can only scavenge the basalts, forming the “West” and “East” divisions we see today.

Stage 06

Copper Formation Today

Bands of copper and other metals (including silver) are formed where the downward “lithostatic” pressure is equaled by the upwelling “hydrostatic” pressure. Where these two meet, copper-bearing minerals start to grow in the pore spaces between sediment grains. These are concentrated in traps such as folds / faults: our target zones.