Talk
Critical Minerals Geology and Exploration

Hydrothermal and structural controls on lead-zinc mineralization at Pine Point, Northwest Territories

Online pre-recorded

Author(s)

R. Adair (Presenting)
Osisko Metals Incorporated
E. Garcelon
Osisko Metals Incorporated
J. Hansen
Osisko Metals Incorporated

The Pine Point Lead-Zinc camp has historically been classified as “MVT-Type”. Wide-spread lead and zinc mineralization is localized into some 100 deposits over a 72-kilometre trend.  Data from roughly 20,000 historical drill holes (1945-2012) have been recovered and converted to a modern digital database and tied into GIS space using LiDAR and DGPS. Field observations and 1326 new drill holes are combined with new airborne gravity gradiometry and airborne magnetic surveys. Ground-based IP and gravity surveys provide further geophysical precision and petrological microscopy, pXRF and µXRF provide new mineralogical detail. These datasets have been modeled in 3D at a regional and deposit scale.

Pine Point deposits are characterized as “Tabular” and “Prismatic” types. Tabular deposits are elongated, with a strata-bound preference to mineralization. Prismatic deposits are characterized by a vertical aspect, often crosscutting multiple stratigraphic units. Both types exhibit sulphide-mineral zonation. Mineralization is hosted in dolomite-altered, lower Devonian carbonate reef and platform carbonates, with the Great Slave Shear Zone, a deep-crustal structure, obliquely transecting Pine Point.   

Early-stage dissolution of primary carbonates and precipitation of secondary dolomite alteration was developed by low-temperature hydrothermal fluids. Alteration shows preference for specific facies within the reef, but new evidence also suggests significant structural controls. Sphalerite, galena, and marcasite mineralization is associated with on-going dissolution and alteration. Alteration is characterized by various textures and stages of hydrothermal dolomitization, some of which are pathfinders to mineralization, and calcification.  Hydrocarbons (bitumen, H2S) present during precipitation of sulphide minerals may have provided a source of sulphur and played a key role in the precipitation process.

It is now demonstrated that the Tabular deposits form as discrete channel ways with significant structural influence as demonstrated by stratigraphic off-sets and vertical fracturing in drill core. These channel ways feed directly into the Prismatic-style deposits where the combination of lithology and fracturing maintained fluid focus and promoted vertical fluid flow and resultant mineralization with related alteration. 

On-going, paleo-dissolution and reprecipitation during the mineralizing process is demonstrated by stratified sedimentary rock consisting of non-soluble material and, locally, sulphide detritus within paleo-cavities. The system was active during and after this internal sedimentation as demonstrated by the development of colloform sphalerite growing within these internal sedimentary rocks. Recent karst, is characterized by till-filled collapse structures unrelated to mineralization.

We classify these deposits as “Carbonate Hosted Pb-Zn” demonstrating structural and stratigraphic control of low temperature hydrothermal alteration and resultant mineralization in the presence of hydrocarbons.