Abstract Systematic changes of major and trace element patterns are found in the footwall hydrothermal alteration of the Brunswick 6 and 12, Heath Steele (B zone), and Halfmile Lake massive sulfide deposits in the Bathurst Mining Camp, New Brunswick. A core of Si alteration, surrounded by Na-Mg and K alterations, occurs in the stringer mineralized zones within the footwall porphyritic and aphyric rhyolitic tuffs and tuffaceous sedimentary rocks of the Nepisiguit Falls Formation at these deposits. Compared to the outer zone (Na-Mg, K alterations), the inner stringer zone (Si alteration) is characterized by relatively high values of Si, K, Ba, Eu, Cu, S, Sb, Sn, Au, and Ag, and relatively low Mg, Na, and REE. In particular, the inner stringer zone (Si alteration) is typified by positive Eu anomalies in its REE patterns and positive Ba anomalies in normalized multielement patterns, as well as high and variable MgO/K 2 O ratios and low Na 2 O/K 2 O (<0.2) ratios, which are distinct from the outer zones (Na-Mg and K alterations). These chemical changes provide vectors toward the overlying massive sulfide orebodies. The alteration patterns and their chemical changes in the stringer zone are best explained by the mixing of high-temperature hydrothermal fluids with seawater, similar to hydrothermal systems on the modern sea floor. Mass-balance calculations indicate that Mg, which is depleted in modern hydrothermal fluids, was added to the altered rocks and probably derived from seawater. Conversely, addition of Si, Ba, Cu, Pb, Zn, As, S, and Fe was probably from a hydrothermal source. Strong positive correlations among Ba/Ba,* Eu/Eu,* and Cu indicate that the Cu mineralization in the stringer zones is closely related to the precipitation of Ba and Eu when the hydrothermal fluid mixed with the seawater permeating below the sea floor. In contrast, Pb- and Zn-rich massive sulfides appear to have precipitated by the mixing of the hydrothermal fluids with ambient cold seawater on the sea floor.

Abstract The concentrations of incompatible elements in felsic volcanic rocks can be correlated with the ore metal ratios of associated volcanogenic massive sulfide (VMS) deposits in various localities worldwide. The felsic rocks are predominantly dacitic to rhyolitic in composition with a calc-alkalic affinity comprising variable proportions of bimodal volcanic rocks thought to have formed in a back-arc extensional environment. They can be categorized into low, mid, and high Th rhyolites. The low Th rhyolites comprise <15 percent of the bimodal suites in the Abitibi (Noranda area). They contain low concentrations of incompatible elements and low Th/Th* (<3) and La n /Yb n (<3). The mid Th rhyolites make up about 15 to 80 percent of the bimodal suites in the Hokuroku and Abitibi (Kidd Creek, Kamiskotia, Matagami, and Manitouwadge) areas. They have medium Th concentrations and moderate Th/Th* (3–8) and La n /Yb n (2–6). The high Th rhyolites constitute >65 percent of the bimodal suites in the Bathurst Mining Camp and the Iberian Pyrite Belt and have high concentrations of incompatible elements as well as high Th/Th* (>8) and La n /Yb n (>4). The enrichment of K and trace elements, such as Pb, Th, and light rare earth elements (LREE), in felsic volcanic rocks is accompanied by an increased Pb content and Pb/Zn ratio in associated VMS deposits, except for some Archean Abitibi deposits. The high Th rhyolites host Pb + Zn-rich deposits with high Pb/Zn ratios (0.3–0.5) in the Bathurst Mining Camp and the Iberian Pyrite Belt. The mid Th rhyolites are associated with Cu + Zn ± Pb deposits with moderate Pb/Zn ratios (0.1–0.3) in the Hokuroku district and some parts of the Abitibi belt (Kidd Creek and Matabi). The low Th rhyolites underlie the Cu-rich VMS deposits with low Pb/Zn ratios (<0.1) in other parts of the Abitibi belt (Noranda). Based on these compositional correlations, three types of VMS deposits can be recognized in felsic volcanic rocks, each having distinct magmatic and tectonic settings. The Noranda-type VMS deposits formed in a back-arc basin behind an immature island arc, which is similar to the Manus back-arc basin in the western Pacific. The low concentrations of incompatible elements in their low Th rhyolites may be related to a depleted source region below a mafic-dominant immature island-arc crust. The Kuroko-type deposits are associated with the mid Th rhyolites that probably originated in a moderately enriched source within a mature island arc, comparable to the Taupo-Havre-Lau back-arc basins in the south Pacific. The relatively high Pb/Zn ratios in the Hokuroku felsic rocks and Kuroko deposits, compared to those of Archean mid Th felsic rocks and associated VMS deposits, are possibly related to relatively large proportions (30–50%) of a felsic component in the mature island-arc crust. The Bathurst-type deposits occur in the high Th rhyolitic terranes where the felsic magmas probably resulted from the partial melting of enriched, felsic-dominant continental crust. They are related to an intracontinental back-arc environment analogous to the Okinawa trough in the northwestern Pacific. The compositional correlations between felsic volcanic rocks and associated VMS deposits imply a genetic relationship. It is speculated on the basis of results from experimental, isotope, and melt and/or fluid inclusion studies that felsic magmas, by degassing ore metal-rich magmatic fluids, contribute large quantities of ore metals to the formation of VMS deposits, in addition to providing heat to drive the hydrothermal convection.

Abstract In the geological record there exists a group of massive sulfide deposits that have been termed “Besshi-type” for their resemblance to the late Paleozoic massive sulfides at the Besshi mine on Shikoku Island, Japan (e.g., Slack, 1993). Besshi-type deposits are characterized by conformable, stratiform, blanket-like sheets of massive pyrrhotite and/or pyrite with variable contents of chalcopyrite, minor sphalerite, and rare galena. Copper is the principal economic metal, and there is subordinate zinc, cobalt, silver, and/or gold. The ores occur in submarine mafic volcanic rocks and associated marine sedimentary rocks including metagraywacke, quartzite, and metapelite that are mostly of deep-water facies. Felsic meta-igneous rocks are rare to absent, and mafic meta-igneous rocks generally are volumetrically subordinate to sedimentary rocks, although in some deposits the former predominate. Besshi-type deposits may form in numerous tectonic settings including back arc basins, rifted continental margins, intracontinental rifts, fore arcs, and sedimented spreading ridges proximal to continental land masses. The sheet-like or tabular morphology of many Besshi-type deposits is due to post-depositional deformation. The Windy Craggy Cu-Co-Au massive sulfide deposit is located at 59°44' N latitude and 137°44' W longitude in the extremely rugged and glaciated terrain of the Alsek-Tatshenshini River area of the St. Elias Mountains, in the northwestern corner of British Columbia (Fig. 1). The deposit crops out on Windy Peak at an elevation of 2,000 m. It was discovered by Frobisher Ltd., a subsidiary of Ventures Ltd., now Falconbridge Ltd., during follow-up of an aerial and regional reconnaissance geological survey of the St. Elias Mountains conducted in 1957 to explore for Triassic massive sulfides similar to the Kennecott deposit in Alaska. Sporadic exploration activity occurred from 1958 to 1980 and led to the conclusion that the property was too remote to be economic. In late 1983, Falconbridge conveyed title to the property to Geddes Resources, which conducted all subsequent exploration. Work between 1988 and 1991 included 4,139 m of underground development and 64,618 m of drilling in 55 surface and 147 underground diamond drill holes. Two large massive sulfide zones, termed the North sulfide body (NSB) and South sulfide body (SSB), were outlined and likely a third zone (Ridge zone) was intersected by drilling. The latest (December 1991) total of proven, probable, and possible reserves is 297.4 million metric tonnes (Mt) grading 1.38 percent Cu at a cutoff grade of 0.5 percent Cu (Geddes Resources Ltd., 1991). The deposit is likely much larger than this as the limits of the NSB, SSB, and particularly the Ridge zone have not been delineated. The NSB alone (to December 1991) contains 138.3 Mt in all categories grading 1.44 percent Cu, 0.22 g/t Au, 4.0 g/t Ag, 0.066 percent Co, and 0.25 percent Zn. Other massive sulfide prospects, including the Tats and X (also referred to as Rime or East Arm) showings, have been identified in the vicinity of Windy Craggy. It is clear that the region has the potential to become a major mining district. However, strong worldwide public and governmental opposition ensued over the proposed development of a mine in a pristine wilderness area surrounded by National Parks and World Heritage Sites. The British Columbia government decided that mining of the deposit was environmentally too hazardous and declared the entire area of one million hectares a “Class A” provincial park. In December of 1994 the United Nations Education, Scientific and Cultural Organization (UNESCO) designated the area a World Heritage Site.