Aldridge Minerals - Yenipazar Compared to Bathurst VMS & Iberian Pyrite Belt

Yenipazar Compared to Bathurst VMS & Iberian Pyrite Belt

The Yenipazar deposit if of volcanogenic massive sulphide (VMS) nature, hosted in mica- and biotite-schist. VMS-deposits form on the sea-floor along zones where metal sulphides vent into the sea from the chimney-like black smokers. The comparison below with other VMS-deposit types shows that Yenipazar is most similar to deposits in the Bathurst district, NE Canada. The Yenipazar deposit is open-folded and only slightly deformed at a scale of few hundred meters (see long section on the Yenipazar page).

High-temperature metamorphism (Late Cretaceous, 90 million years ago) led to re-mobilization of the ore minerals, originally deposited on the sea floor. Re-mobilization took place on a scale of centimeters to perhaps one meter, and led to growth of larger ore mineral grains, which can potentially be more cost-efficiently separated from the host rock than in usual VMS deposit.

The Yenipazar VMS-orebody is clearly ranked within the felsic siliciclastic (F-S) group of Barrie & Hannington (1999), addressing the felsic (= quartz-rich) to calc-alkaline volcanic rocks and clayey-silty sediments in the host rocks. Sediments are by volume more important than volcanics at Yenipazar. The VMS-deposits in the Bathurst district of NE Canada and in the Iberian Pyrite Belt also belong to the F-S group.

The F-S group hosts the largest VMS-deposits in the World, with a World average size of 23.7 Mt. This is about 3 times the size given in the last 43-101-compliant study for the Yenipazar deposit (data as of Jan 2007), but the strike extent has subsequently been shown to be 3 times longer than indicated in this study, at similar metal grades, thicknesses, and widths. The according 43-101 resource update for Q2 2008 is expected to report much higher resources than previously indicated.

Among all VMS-types, the F-S group has the lowest ratio of copper to lead + zinc, which is also observed at Yenipazar. For example, the mined-out Aznalcollar deposit in Spain is reported with 0.49 % Cu, 2.14 % Zn, 1.04 % Pb, 44 g/t Ag, 0.5 g/t Au (Hannington et al. 1999), which is metal-proportionally similar to Yenipazar, although with somewhat higher grades for Cu, Zn, Ag, and somewhat lower grades for Pb, Au.

F-S-group VMS-deposits are generally described as barite-rich, but at Yenipazar, barite is rare. The same is observed at Bathurst, making Bathurst the closest correlative.

An outstanding feature at Yenipazar is the proportionally high content of gold. This is counter-trend for the F-S group, wherein barite and gold are seen positively correlated, and within that trend, Yenipazar should be markedly gold-poor. However, some VMS-deposits are clearly enriched in gold versus base metals, ascribed to special conditions during deposit formation. This may include magmatic (epithermal gold) contributions to the metal-depositing fluids (Hannington et al. 1999).

In terms of the geotectonic setting, F-S group VMS-deposits are clearly related to active continental margins, in rifts above a subduction zone. These rifts may occur in intra-arc or back-arc settings, but are underlain by continental crust. The subsiding crust in these extensional zones is invaded by the sea, and VMS forms on the sea floor.

Central Anatolia represents a continental fragment (terrane) that formed an island in the Mid-Cretaceous Tethys Ocean, where it was subjected to collision, crustal thickening, and metamorphism at about 90 Ma (Oczlon 2006, Terrane Map of Europe, see Start Page of the Aldridge website). Possibly, the preceding period of convergence with subduction of oceanic lithosphere under the continental terrane that now carries the Yenipazar deposit, triggered supra-subduction-zone-rifting and VMS-formation. If so, the Yenipazar deposit may only be 10 Ma older than the (peak) metamorphic age of 90 Ma determined for the Central Anatolian terrane.