The Pine Point deposits are carbonate-hosted lead-zinc sulphide deposits with aspects of Mississippi Valley-Type (“MVT”). MVT deposits and a broader class of deposits called “sediment-hosted Pb-Zn” deposits (Leach et al., 2010).
Mineralization is hosted in three distinct deposit types:
1. Prismatic Deposits–Prismatic deposits demonstrate considerable vertical continuity but with limited lateral extent and are discordant. Mineralization is coarse to medium grained. These deposit types are further divided in to normal and abnormal prismatic deposits based on their relative stratigraphic position in the sequence. They contributed greatly to the Pine Point historical production as they contained very high-grade base metal grades and thicknesses.
2. Tabular Deposits–Laterally continuous, semi-concordant mineralized zones mostly restricted to a specific carbonate horizon.
3. N204 Deposit–N204 mineralization consists of fine crystalline mineralization deposited within the porosity ofstrati-bound layersbelow the mainsequence known as the B-spongy horizon where intense dissolution resulted in the development of a fine dolomite breccia. This type of deposit has to date only been identified at N204.
Prismatic Deposits
Prismatic deposits are generally high-grade and can contain up to 50% combined Pb-Zn, depending on the amount of sulphide mineralization present. These deposits are vertically continuous for up to 60m, and laterally restricted, generally 15-50m, but can be up to 140m wide. Metal zonation is present with a galena-rich core (Pb/Pb+Zn >0.3) enveloped by a more sphalerite-rich outer zone.
Prismatic deposits generally initiate at the Pine Point/Sulphur Point Formation facies transition and extend upwards through a dolomitized stratigraphic section, including upper sequences such as the Slave Point Formation. Abnormal prismatic deposits generally initiate within the lower stratigraphic sequences and extend upward.
These types of deposit generally contain blocks of overlying and adjacent stratigraphicmaterial. Such blocks can exhibit angular and dissolution textures. Cavities and vugs are common and abundant internal sediment accumulations are observed to fill earlier open spaces. These sediments are the residues of intense hydrothermal dissolution consisting of insoluble carbonaceous debris, argillite components, and sulphide material. It is believed that these sediments are remnants of the intense hydrothermal dissolution process associated with sulphide emplacement.
Tabular Deposits
Tabular deposits develop in distinct biomicrite facies carbonate sequencesin the lower Sulphur Point Formation.They are laterally continuous,following the general carbonate reef trend. They most likely followingthe increased porosity and permeability generated by hydrothermal fluid flow along distinct ‘channels’ or fluid pathways in suitable carbonate sequences. Other suitable host lithologies,e.g. the ‘B-Spongy’,are potential exploration targets.
Tabular deposits are vertically restricted relative to Prismatic Deposits and are generally zinc-rich (Pb/Pb+Zn) <0.2 with local lead-enrichment. They are lower-grade relative to prismatic deposits due to less massive and sporadic sulphide development. Zinc and lead grades decrease outwards from the core of hydrothermal fluid pathways (channels) and distally from interpreted local ‘feeder’ structures.
N204 Deposit
A related type of mineralization is found at N204 where tabular-like mineralization occurs in a lower part of the barrier reef stratigraphy in a horizon named the “B-spongy horizon” (Cominco Ltd. terminology). Here, precipitation of fine-crystalline dolomite resulted in the preferred dissolution of macro fossil components resulting in the development of a distinct moldic porosity. Mineralization at the N204 deposit is wholly confined to this dissolution horizon.
Mineralization
Mineralization at Pine Point is relatively simple, consisting of zinc, lead and iron sulphides occurring ina dolomitized, carbonate barrier reef complex. Sulphides consist of sphalerite and galena with subordinate marcasite and pyrite. Mineralization occurs as both openspace fillings and replacement of dolomite. The following types are documented:
1. Fine replacive sphalerite. This style of mineralization is common and present in tabular deposit typesand adjacent to more pervasive mineralization. It varies from massive to disseminated replacement sphalerite. The more massive replacement mineralization allows for the development of discrete banded colloform sphalerite masses.
2. Colloform sphalerite. Colloform mineralization develops with increased dissolution of the host carbonates with marginal replacement disseminations and fine filaments. The colloform mineralization is extensive at the core of tabular deposits. Well-developed colloform sphalerite decreases away from the core of the linear tabular depositsand is also present in the prismatic deposits.
3. Finely to coarsely-crystalline, replacive and openspace filling sphalerite mineralization. Sphalerite crystals up to 12mm are recorded in clean dolomitized biomicrites. There are limited and local amounts of associated marcasite.
4. Finely to coarsely-crystalline galena. Galena crystals typically define the last paragenetic stage of the depositional process and can be locally concentrated in galena-rich areas. Typically,however, galena is present in subordinate amounts compared to sphalerite.
5. Massive sulphides. Prismatic mineralization is generally massive, consisting of 100% carbonate-replacement sulphideswith a complete grain size spectrum from microscopic to mega crystalline sphalerite and galena mineralization. Multiple fluid phases allow for re-dissolution/precipitation and the generation of internal ‘openspace’ colloform mineralization, often spectacular and unique to the Pine Point District.Complex sulphide mineralization.
6. Complex sulphide mineralization in Prismatic Deposits also consists of massive sulphide replacing polymictic carbonates consisting of multiple ‘fallen’ or collapsed blocks from the overlying strata of the upper sequence carbonates, e.g.,large blocks consisting of Slave Point Formation and indeed the replacement of internal dissolution sediments developed during the dynamic formation of the chimney-like, vertically elongate massive sulphide deposits,which define typical Prismatic Deposits. There are local galena-rich zones, typically massive to coarsely-crystalline. 7. Heterogenous massive sulphides. Predominantly sphalerite-rich massive sulphides exhibiting characteristics of both replacive massive sphalerite but with a later more coarse-crystalline andslightly higher temperature sphalerite phase overgrowth. This appears to occur in several small prismatic deposits in the eastern portion of the Main Trend.
8. High temperature sulphides. Higher temperature, finely-crystalline, crypto-colloform ‘black’ sphalerite mineralization is typical of some North Zone prismatic deposits. This style is best developed in internal grey carbonate sediment with a ‘veines bleues’ dolomite association.N204 type mineralization.
9. The N204 mineralization is fine-grained, sphalerite dominated mineralization consisting of fine-replacive and minor fine to medium open space sphalerite crystals within moldic porosity.
