Carbonatite
Carbonatite
Sawed piece of drill core showing the carbonatite that was found in DDH Thor-246. Although these can appear similar to carbonate found in the epithermal deposit, these are enriched in CaO releative to Mg and Fe2O3.
Why are Carbonatites Showing Up with the Lamprophyres?
Carbonatites and lamprophyres commonly occur together because they originate from low‑degree partial melting of a metasomatized mantle, producing melts that are:
• Highly alkaline
• Extremely volatile‑rich (H₂O, CO₂, F, Cl)
• Enriched in incompatible elements (Ba, Sr, REEs, K, Rb)
• Prone to melt immiscibility — splitting into a silicate melt
(lamprophyre) and a carbonate melt (carbonatite)
The suspected source of the carbonatites at Thor can is attributed to the I-1 Intrusive body, that is also calcium and sodium-rich.
(lamprophyre) and a carbonate melt (carbonatite)
The suspected source of the carbonatites at Thor can is attributed to the I-1 Intrusive body, that is also calcium and sodium-rich.
Heavily carbonatized sediments with eyes of fuchsite along edges of lamprophyre dyke. These areas are prone to gold values (up to 0.5 g/t Au), and historically fuchsite is a pathfinder to gold mineralization
Ternary diagram showing the difference in carbonate composition - Carbonatite versus epithermal carbonate.
What is a Carbonatite?
Geochemistry of Carbonates
At Thor, the carbonatite is best understood as a carbonate‑rich melt component associated with the lamprophyre intrusions — not a large, independent carbonatite plug or sill.
This interpretation is strongly supported by global analogues where lamprophyres and carbonatites form together from volatile‑rich, mantle‑derived magmas.
A carbonate‑rich melt phase genetically linked to the lamprophyre intrusions — likely present as carbonate melt droplets, segregations, or carbonatite‑style alteration zones within and around the lamprophyre dykes. It is not yet mapped as a standalone carbonatite body, but the geochemical and alteration evidence strongly supports a lamprophyre–carbonatite association, just like those documented in other alkaline, mantle‑derived intrusive systems worldwide.
A carbonate‑rich melt phase genetically linked to the lamprophyre intrusions — likely present as carbonate melt droplets, segregations, or carbonatite‑style alteration zones within and around the lamprophyre dykes. It is not yet mapped as a standalone carbonatite body, but the geochemical and alteration evidence strongly supports a lamprophyre–carbonatite association, just like those documented in other alkaline, mantle‑derived intrusive systems worldwide.
A simple ternary plot can differentiate between carbonates that are associated with the lamprophyre dykes and those that are associated with the epithermal veins at Thor. The carbonatites that are associated with the lamprophyre bodies have much more calcium than the carbonates that are associated with the epithermal mineralization.
Carbonate‑rich melt lenses or segregations within the lamprophyre system Global analogues show that lamprophyre magmas often contain calcite‑rich ocelli — droplets of carbonate melt that later solidify. These are the hallmark of lamprophyre–carbonatite associations, and some of them can be seen in the photo to the left.
Thor’s lamprophyres produce: • Intense carbonate flooding • Bleached, CO₂‑rich alteration zones • Strong sulphidation and reaction rims This alteration style is consistent with carbonate‑bearing magmas interacting with metasedimentary host rocks
Carbonate‑rich melt lenses or segregations within the lamprophyre system Global analogues show that lamprophyre magmas often contain calcite‑rich ocelli — droplets of carbonate melt that later solidify. These are the hallmark of lamprophyre–carbonatite associations, and some of them can be seen in the photo to the left.
Thor’s lamprophyres produce: • Intense carbonate flooding • Bleached, CO₂‑rich alteration zones • Strong sulphidation and reaction rims This alteration style is consistent with carbonate‑bearing magmas interacting with metasedimentary host rocks