Multiple Hydrothermal Processes in Footwall Units of the North Range, Sudbury Igneous Complex, Canada, and Implications for the Genesis of Vein-Type Cu-Ni-PGE Deposits

Abstract

Systematic regional sampling along the contact zone of the 1.85 Ga age Sudbury Igneous Complex with the Archean Levack Gneiss footwall in the North Range of the Sudbury structure revealed textural, mineralogical, and fluid inclusion systematics of post-Sudbury Igneous Complex hydrothermal processes that affected the various lithologies. At late stages of emplacement of the Sudbury Igneous Complex and formation of magmatic Fe-Ni-Cu sulfide deposits a partial melt from the Levack Gneiss invaded the contact zone. This partial melt is revealed by small microdikes and irregular bodies of granophyric quartz-plagioclase with megacrysts of hornblende, clinopyroxene, and titanite. Plagioclase-hornblende equilibrium was established at 750°to 800°C and 1.10 to 1.55 kbars pressure, corresponding to about a 4-to 6-km depth under lithostatic conditions. F/Cl wt percent ratios around 15 for accessory apatite and hornblende indicate that a Cl-rich fluid phase separated during the crystallization of the footwall granophyre: this is expressed as miarolites. The Cl-rich fluid (50 wt % NaCl equiv salinity) was trapped as primary fluid inclusions in quartz at around 480°C minimum temperature and around 1.1 kbars minimum pressure during supercooling. These inclusions are rich in Ca, Fe, Mn, and K, as well as Na chloride. This fluid may have interacted with earlier primary magmatic sulfide, causing remobilization and reprecipitation of Cu-Ni-platinum-group elements (PGE) in veins and disseminations in the footwall. These veins are parallel to the Sudbury Igneous Complex-footwall contact and are characterized by chalcopyrite, pentlandite, millerite, magnetite, stilpnomelane, ferropyrosmalite, epidote, and chlorite. Michenerite, moncheite, merenskyite, froodite, insizwaite, sobolevskite, gold, and Bi-Ni sulfides are associated with sulfides. Epidote, quartz, actinolite, and chlorite are common in the alteration selvages of the veins. Compositions and assemblages of platinum-group minerals (PGM) indicate their precipitation below 575°to 485°C. Primary, highly saline fluid inclusions (about 40 wt % NaCl equiv) in quartz indicate crystallization at 400°to 480°C and around 1.6 kbars minimum T and P, respectively. Late carbonate-epidote-actinolite-chlorite veins and alteration overprinted the earlier assemblages at about 300°to 400°C, with some bornite, millerite, native silver, and other Bi sulfides. The second stage of hydrothermal activity is characterized by regional carbonic-aqueous (NaCl-CO 2-CH 4-H 2 O-type) immiscible fluids that were trapped as secondary inclusions in quartz from various lithologies. No mineralization is related to this stage along the North Range. Boiling of these fluids took place during a pressure drop from lithostatic to hydrostatic conditions during uplift from about a 5-to 6-to a 3-to 4-km depth at 300°to 350°C. High-(20-26 wt % NaCl equiv) and low-salinity (6-12 wt % NaCl equiv) fluids coexisted with different carbonic species contents. The predominant north-south and northwest-southeast orientations of fluid ...

Ore metal redistribution by hydrocarbon–brine and hydrocarbon–halide melt phases, North Range footwall of the Sudbury Igneous Complex, Ontario, Canada

“…1c, d). Although volumetrically insignificant when compared to the massive sulfide veins, the alteration veins sampled for this study are widespread in footwallstyle deposits and have been documented at all footwallstyle deposits along the northern margin of the SIC (Li 1993;Farrow 1994;Molnar et al 2001). The alteration veins are rich in PGE and Au; they may contain up to 15 ppm Au, 7 ppm Pd and 5 ppm Pt on a bulk rock basis (Hanley 2002).…”

“…3a) [Note that brine inclusions of primary origin (without coexisting hydrocarbon inclusions) were described in detail by Li (1993), Farrow (1994) and Molnar et al (2001)]. Commonly, inclusions in the assemblage contain both a hydrocarbon phase and brine within the same inclusion and show highly variable phase ratios (Fig.…”

“…Major points of evidence supporting a hydrothermal model for the ores include: (1) the occurrence of high salinity fluid inclusions in both sulfides and silicate alteration minerals that contain ore metals (e.g., Ag, Cu; Farrow 1994); (2) the occurrence of metal halide minerals within the PGE-Au-rich sulfide vein assemblages (e.g., an unnamed Pd-Bi-Cl phase; Li 1993); (3) the occurrence of primarily low temperature Pt and Pd minerals (e.g., <600°C; tellurides, bisthmuthide, stannides) hosted in chlorine-rich alteration assemblages along the edges of massive sulfide veins rather than in the massive sulfide veins themselves (Li 1993;Farrow 1994); and (4) the presence of oxidized and intensely altered (?Cu-Au-Pt-Pd-leached) zones of high Ni-content ores along the SIC-footwall contact (''epidote-zone'' mineralization; Farrow 1994). The most comprehensive fluid inclusion study in support of the hydrothermal model was conducted by Molnar et al (2001). A summary of the major contributions to the hydrothermal model can be found in Table 1; these will be referred to in light of our new observations below.…”

Hydrothermal Alteration in the Main Sulfide Zone at Unki Mine, Shurugwi Subchamber of the Great Dyke, Zimbabwe: Evidence from Petrography and Silicates Mineral Chemistry

“…Olivine melagabbronorites, the host rocks in the Tootoo and Mequillon magmatic sulfide deposits, were pervasively altered to hydrous mineral assemblages dominated by chlorite, tremolite-actinolite, and relict late-magmatic hornblende that are consistent with greenschist facies metamorphism [22]. Large-scale and very saline hydrothermal fluid activity is also interpreted to have affected rocks of the Sudbury Complex and in the process caused remobilization of both base metals and PGEs [105,106].…”

Secondary alteration of the impactite and mineralization in the basal Tertiary sequence, Yaxcopoil‐1, Chicxulub impact crater, Mexico

“…Ivanov and Deutsch 1999). Seawater, groundwater, deep-formational brines and magmatic fluids from the melt sheet are the fluid sources recognized at other impact sites (McCarville and Crossey 1996;Ames et al 1998;Farrow and Watkinson 1999;Molnar et al 2001;Ames 2002). The circulation of fluids is controlled by the permeable impactites, syn-crater faults and paleotopography (Ames et al 2000).…”