Volcanogenic Massive Sulfide Exploration Research Articles

Zircon and the role of magmatic petrogenesis in the formation of felsic-hosted volcanogenic massive sulfide (VMS) deposits: a case study from the mid-Paleozoic Yukon-Tanana terrane, northern Canadian Cordillera

Magmatism is a critical component in sustaining hydrothermal convection and metal transport during the formation of volcanogenic massive sulfide (VMS) deposits. Previous studies of magmatic petrogenesis in VMS systems have demonstrated that ore-related volcanic rocks have distinct whole-rock geochemical and isotopic signatures (i.e., high HFSE, REE, Th, εHf-Nd, zircon saturation T) relative to barren volcanic rocks, which supports models of elevated crustal heat flow during periods of ore deposition; however, the petrologic characteristics and intrinsic parameters (e.g., T, fO2) related to these magmatic events in VMS districts remain poorly understood. Arc–back-arc assemblages from the mid-Paleozoic Yukon-Tanana terrane are well-characterized and include the Finlayson Lake VMS district, which is host to several felsic-hosted deposits (e.g., Kudz Ze Kayah, GP4F, Wolverine) that were generated in a peri-Laurentian continental back-arc tectonic setting. In this study, zircon from back-arc and coeval arc rocks in the Yukon-Tanana terrane was used as a proxy for primary magma formation conditions that generated VMS-proximal and VMS-distal stratigraphy. Our results indicate that zircon grains in VMS-proximal environments have unique textural, geochemical, and isotopic characteristics (e.g., low-aspect ratios, greater abundance of zircon-phosphate intergrowths, Th/U > 1, Zr/Hf > 80, Tzrc > 780 °C, εHfi > –7) that are clearly distinguished from zircon in VMS-distal rocks in both the back-arc and arc settings (Th/U < 1, Zr/Hf < 80, Tzrc < 780 °C, εHfi < –7). These signatures correlate to VMS-proximal magmas that were hotter, less fractionated, and contained greater juvenile melt contributions compared to VMS-distal magmas and reflect a series of high-flux magmatic events that directly correspond to the early tectonic development of Yukon-Tanana terrane. Moreover, this study underscores the importance of mineral-scale petrology, geochemistry, and geochronology in defining the primary magmatic conditions that generated VMS-related felsic rocks and highlights the utility of zircon as a prospectivity tool in both grassroots and brownfields VMS exploration.

Use of semi-volatile metals as a new vectoring tool for VMS exploration: Example from the Zn-rich McLeod deposit, Abitibi, Canada

Volcanogenic massive sulfide (VMS) deposits are small targets (100's of meters) hosted in a hectometric to kilometric-scale zoned alteration halo, comprising narrow proximal chlorite and wider distal sericite zones. For exploration, identification of the distal fine-grained sericite halo related to fertile VMS systems is critical but remains challenging. Sericitization is a low-temperature hydrothermal alteration and its geochemical signature could be very similar to clay assemblages produced as the results of simple low-temperature prolonged seawater interaction with volcanic rocks on the seafloor. Currently, classical lithogeochemical methods (e.g., mass balance, element ratios) are not very efficient to decipher sericite alteration related to distal fertile VMS systems. However, semi-volatile metals have good potential as pathfinders, as they have a wider dispersion than major, or trace elements commonly used due to their enhanced mobility in hydrothermal fluids. New analytical improvements, involving four-acid digestion and advanced ICP-MS technology, now allows the accurate determination of semi-volatile metals at the ppb level.Using the Zn-rich McLeod deposit in the Matagami district (Abitibi, Canada) as a case study, we tested first the representativeness and advantage of the new analytical method, and secondly, the capacity of the semi-volatile metals for vectoring exploration. The new method is both accurate and precise and provided good resolution with low detection limits. The performance of classical lithogeochemical methods was compared with semi-volatile metal distribution (As, Se, Cd, In, Sn, Sb, Te, Hg, Tl, Bi) in the footwall rhyolite. Although the classical tools efficiently identified both the proximal chlorite and distal sericite zones, most of them (except Rb/Sr) cannot efficiently vector, as there is no systematic increase or decrease towards the mineralization. Conversely, overlapping alteration halos were identified using semi-volatile metals. The proximal signature (chlorite zone) is characterized by enrichment of Sb, Li ± Mo, W and U. The distal signature (sericite zone) is defined by successive appearance of higher values of Sn, W, and Tl up to 750 m, 1000 m and 1400 m away from the mineralization, respectively. This zoned spatial distribution of semi-volatile metals clearly allows better localization of a given altered sample within a wide and distal alteration halo, thus providing a solid vectoring tool for VMS exploration. This is especially true since the signal of semi-volatile metals extends far beyond both the visual sericite alteration (up to 200 m from mineralization) and classical lithogeochemical tools (up to 1000 m away). Specifically, the Tl/Co ratio records the widest footprint of the mineralization, up to 1400 m away from the deposit. It is well known that Tl is enriched in Zn-rich VMS. Thallium in the sericite alteration halo is here considered as an indicator for discriminating fertile volcanogenic hydrothermal systems from barren low-temperature convective cells.

Drill Targeting with 3-D Seismics for Volcanogenic Massive Sulfide Exploration in the Flin Flon Mining Camp

A 17-km2 3-D seismic survey was conducted in 2007 within the Flin Flon volcanogenic massive sulfide (VMS) mining camp as part of the Targeted Geoscience Initiative-3. The resultant 3-D images show strong reflectivity associated with the ore-hosting mine horizon and prominent reflections attributed to the known ore zones. Structural repetition of the mine horizon is clearly identified in the seismic images with at least three levels identified. The 3-D seismic images have been used in conjunction with detailed geologic and geophysical drill hole logs to identify new exploration drill targets. Results from the first three seismic-based exploration drill holes are presented. The drill holes encountered reflective geologic contacts at depths within 3 to 8% of those predicted from the 3-D seismic images. In the first case, a gabbro of no economic significance was encountered at the target depth. In the second case, a highly altered mafic volcanic panel with stringer mineralization was identified sitting blind beneath surface exposures of sandstone. In the third case, the target turned out to be an additional structural level of the mine rhyolite, which provides a new horizon for further exploration. A small massive sulfide ore lens was discovered during follow-up drilling around the third target. These results demonstrate that seismic methods can be successfully applied for mineral exploration in areas of existing infrastructure and cultural noise.

Till Geochemistry in West-Central Manitoba: Interpretation of Provenance and Mineralization Based on Glacial History and Multivariate Data Analysis

Till geochemical datasets from archived samples in west-central Manitoba are interpreted using multivariate data analytical techniques such as principal component analysis and pathfinder element index methods, combined with a spatial representation of the data in a geographic information system (GIS). Results show that carbonate till derived from Hudson Bay, as expressed by the (Ca + Mg)/Na ratio, is found predominantly east of Leaf Rapids and extends south into the Northeastern Kisseynew Domain. A 30- to 70-km-wide zone is documented beyond the limit of dissolvable carbonate dispersal that contains till of Labradorean provenance with low Ca-Mg-Mn-Te concentrations, noncalcareous till of Keewatin provenance, and silty calcareous till at depth. The variation in till provenance, together with the predominance of southwesterly ice-flow indicators, suggests that carbonate dispersal occurred prior to deglaciation, and that surface tills in the zone of confluence between Labradorean and Keewatin ice are likely the result of recycling of calcareous tills and/or carbonate-leached sandy tills, mainly by Keewatin ice. The newly defined limits of carbonate and Ca-rich till, typically used to assess provenance and glacial transport, provide a new framework for evaluating the significance of till geochemical patterns when drift prospecting over the Trans-Hudson orogen. Several regional- to local-scale dispersal trains from geochemically distinct bedrock sources are discussed in terms of elemental association, glacial transport characteristics, and potential bedrock sources. The multivariate statistical approach combined with GIS mapping also highlights new areas with small multi- or single-element enrichments that may be of further interest for volcanogenic massive sulfide exploration or for potentially more detailed drift sampling.

Using Physical Volcanology, Chemical Stratigraphy, and Pyrite Geochemistry for Volcanogenic Massive Sulfide Exploration: An Example from the Blake River Group, Abitibi Greenstone Belt,

An innovative approach to enhance volcanogenic massive sulfide (VMS) exploration in regions outside of mining camps is to first use physical volcanology with litho- and chemostratigraphy to establish the location of effusive centers in the volcanic units and use pyrite geochemistry in sulfide-bearing stratified intervals with whole-rock geochemistry in the underlying volcanic units to identify hydrothermal upflow zones. This methodology is illustrated by this study in the Archean Blake River Group within the Abitibi greenstone belt of Quebec and Ontario. The Blake River Group contains numerous VMS deposits, yet large segments remain underexplored, including the Hebecourt Formation which contains four tholeiitic units that range from basalt to rhyolite in composition. Effusive centers are located for three felsic units and subunits: (1) low Ti (porphyritic) subunit of the main rhyolite, (2) high Ti (aphyric) subunit of the main rhyolite, and (3) the upper rhyolite, and for a basaltic andesite unit. Stringer and disseminated Zn-Cu mineralization occurs within the flank breccia of the low Ti rhyolite dome. An inferred vent area for an overlying basaltic andesitic unit has also been identified in this area, illustrating the coincidence of hydrothermal upflow zones with volcanic vents. LA-ICP-MS analysis of pyrite grains from several sulfide-bearing stratified intervals indicates two broad areas of higher Cu, Zn, Au, and Ag contents. The eastern region corresponds to known volcanic vents and mineralization. The western region also indicates upflow of Cu-bearing hydrothermal fluids and corresponds to a possible effusive center for the high Ti subunit. The western region does not contain known mineralization at lower stratigraphic positions, but it has not been thoroughly explored.

Precise U-Pb Geochronology of the Matagami Mining Camp, Abitibi Greenstone Belt, Quebec: Stratigraphic Constraints and Implications for Volcanogenic Massive Sulfide Exploration

The Matagami mining camp in the northern Abitibi greenstone belt of Canada contains 19 known Archean volcanogenic massive sulfide (VMS) deposits, 11 of which have collectively produced 46.5 Mt of zinc-rich ore to date. The VMS deposits occur in three NW-SE– to WNW-ESE–oriented trends called the north flank, the south flank, and the west camp, which are composed of a felsic to mafic volcanic sequence cut by mafic to intermediate, synvolcanic sills and dikes. In order to clarify stratigraphic relationships between the south flank and the west camp, and to constrain the temporal evolution of volcanic activity, six new high-precision U-Pb zircon ages have been obtained. These data show that the total duration of felsic volcanism in the south flank was no more than 2.5 m.y., with the rhyolites extruded in the following order: Watson Rhyolite (2725.9 ± 0.8 Ma), Bracemac Rhyolite (2725.8 ± 0.7 Ma), Dumagami Rhyolite at the Perseverance Mine (2725.4 ± 0.7 Ma), and Dumagami Rhyolite in the Orchan West VMS deposit area (2724.9 ± 0.7 Ma). A hiatus in effusive volcanism is represented by the Key Tuffite, an important marker horizon in the camp. The hiatus probably lasted on the order of 0.5 m.y. Significantly, the rhyolite from the footwall of the Caber VMS deposit in the west camp has an age of 2725.9 ± 1.2 Ma, identical to that of the Watson Rhyolite on the south flank.

Primitive Permo-Triassic volcanism in the Canadian Cordillera tectonic and metallogenic implications

Volcanogenic massive sulfide deposits of various ages, types, and geochemical affinities occur within allochthonous and para-autochthonous terranes of the Cordillera of western Canada. The terrane affiliation, age, and chemical association of volcanic rocks can be used as a guide in the exploration for volcanogenic massive sulfide mineralization. The Kutcho massive sulfide deposit occurs within volcanic rocks of the Kutcho assemblage, in the fault-bounded King Salmon allochthon in northern British Columbia. The Kutcho Creek deposit is characterized by a Permo-Triassic age of mineralization and primitive chemical and radiogenic isotope compositions of the host rocks which are distinct from those of other volcanogenic massive sulfide deposits in the Canadian Cordillera. The Kutcho deposit is interpreted to have formed within a primitive intraoceanic are environment, distinct from the setting ascribed to more typical felsic volcanic-hosted (kuroko) massive sulfide deposits. The age, mineralogy, and chemical and isotopic compositions of rocks from the Kutcho assemblage are comparable to those of two other fault-bounded silvers in the Cordillera, the Sitlika assemblage and the Venables Valley-Red Hill area. These similarities suggest that rocks from the three areas may have formed within the same period and tectonic environment; as such, the latter two areas are prospective for volcanogenic massive sulfide exploration in the Canadian Cordillera.

Spherulitic rhyolites of the Archean Blake River Group, Canada; implications for stratigraphic correlation and volcanogenic massive sulfide exploration

Based on the distinctive textural and chemical character of highly spherulitic rhyolites in the Late Archean, volcanogenic massive sulfide-rich, Blake River Group of Quebec, it is proposed that they represent key beds which may be used to infer the age relationships between the three subgroups (Rouyn-Pelletier, Misema, and Noranda) into which the Blake River Group is divided in this area. These rhyolites occur as flow and fragmental (volcaniclastic, probably pyroclastic) facies, both of which contain crystallization spherulites. They occur as three units, a flow facies exhibiting parallel-agglomerated lath-shaped plagioclase crystals (the Fish-roe rhyolite), a fragmental spherulitic rhyolite which is aphyric, and a second, very local, flow which is quartz-plagioclase porphyritic. Chemically, however, the three units are identical and distinct within the Blake River Group stratigraphy.The Ti, Y, Yb, and Zr contents are higher in the spherulitic rhyolites than in the other rhyolites in the Blake River Group, whereas the La content is similar between the two rhyolite populations. These values translate into higher Ti/Zr, and lower Zr/Y and La/Yb, ratios for the spherulitic rhyolites and result in their being important stratigraphic marker units in the group in Quebec. Statistical analyses of the geochemical data from the rhyolites in the Blake River Group show that there is a 95 percent probability that the spherulitic rhyolite analyses represent a single genetically related population and may, in fact, be a single stratigraphic unit.The occurrence of the fragmental highly spherulitic rhyolite in the andesitic Misema Subgroup and in the bimodal andesitic-rhyolitic Noranda Subgroup implies that these two domains formed, at least in part, concurrently. The same conclusion can be drawn for the basaltic Rouyn-Pelletier Subgroup and the Noranda Subgroup, as the Fish-roe rhyolite occurs in both these domains. This in turn suggests that a complex interplay of contemporaneous magmatic systems, rather than a single vertically stacked evolutionary system, was responsible for the formation of the Blake River Group and its volcanogenic massive sulfide deposits.