Harold L. Gibson

Caldera-forming processes and the origin of submarine volcanogenic massive sulfide deposits

Certain volcanogenic massive sulfide (VMS) ore deposits form in submarine calderas. This association is well known, but the link between caldera formation and the origins of the deposits remains poorly understood. Here we show that the size and location of a VMS deposit within a submarine caldera may be determined by how and when the caldera formed. These spatial-temporal conditions control development of the hydrothermal system associated with the VMS deposit. We propose that caldera opening along outward-dipping faults promotes magma degassing, seawater influx, and high-temperature leaching, resulting in a metal-rich hydrothermal fluid. These outward-dipping faults are considered to provide critical pathways for ore-forming fluids responsible for some caldera-hosted VMS deposits and may also be fundamentally important for the formation of many other caldera-hosted ore deposit types.

Impact-Generated Hydrothermal System — Constraints from the Large Paleoproterozoic Sudbury Crater, Canada

The 1848 Ma impact-generated hydrothermal system in the ∼200-km-diameter Sudbury structure in Canada is sexceptionally well preserved and provides the opportunity to study potential fossil ecosystems associated with impact craters. The hydrothermal alteration fingerprint at the Sudbury impact site is preserved for ∼1 km below the melt sheet and ∼2 km above. The system was capable of producing sufficient heat and fluid flow to form sinter deposits on the crater-floor. Fluid-rock interaction and resultant alteration mineral products record the waxing and waning phases of a complex hydrothermal system within the impact crater with temperatures in the basin ranging from 250–300°C down to ambient. Below the melt sheet fluid-rock interaction took place at <420°C. The exceptional preservation of the Sudbury impact structure including fractured and shocked basement rocks, melt sheet, impact-related crater-fill breccias, chemical sediments on the crater-floor and post impact sedimentation, yields significant new insights into the physical, chemical and potentially the biological framework of impact-generated hydrothermal systems in large craters. Significant to the development of microbial niches is defining the lower temperature regimes (<120°C) of the habitable zone. In the Sudbury basin from base to top, lies a 1.4-km-thick sequence of suevite (Onaping Formation) that has undergone extensive water-rock interaction manifested as regionally extensive semiconformable alteration zones, a thin ∼ 14-m-thick exhalative-sedimentary sequence (Vermilion Formation) and in a metal-enriched hydrothermal plume extending another <1 km into the post-impact basin sediments (Onwatin Formation). The hydrothermal signature includes basin-wide semiconformable alteration zones defined by silicification, albitization, carbonatechlorite alteration in the Onaping Formation. Also present are discordant alteration zones with focussed fluid flow which produced local higher temperature perturbations imposed on the more extensive lower temperature (<250°C) alteration zones within the crater-fill sequence. The Vermilion Formation represents a subaqueous hydrothermal vent complex with a proximal hydrothermal Ca-Fe-Mg-Mn carbonate mound facies containing replacement type Zn-Pb-Cu-Fe mineralization, a distal finely laminated carbonate facies, or “carbonate-facies iron formation”, buried by distal turbidite sediments. Prolonged post-mineralization diffuse fluid flow and unfocussed low temperature emanation of hydrothermal plumes and the Fe-Mn-rich distal carbonates produce favourable habitats for thermophilic microorganisms.

The Horne Mine: Geology, History, Influence on Genetic Models, and a Comparison to the Kidd Creek Mine

The Horne mine was truly a world class Cu and Au deposit. Between 1927 and 1989, it produced some 260 t of Au and 1.13 Mt of Cu from 53.7 Mt of ore that averaged 2.22% Cu, 6.1 g/t Au and 13 g/t Ag. The total value of Au and Cu production from the Horne deposit at metal prices of US

TRACE ELEMENT GEOCHEMISTRY AND PETROGENESIS OF FELSIC VOLCANIC ROCKS ASSOCIATED WITH VOLCANOGENIC MASSIVE Cu-Zn-Pb SULFIDE DEPOSITS

300/oz Au and US

Vitric Compositions in the Onaping Formation and Their Relationship to the Sudbury Igneous Complex, Sudbury Structure

1.00/lb Cu is an outstanding US

A comparison of the Horne volcanogenic massive sulfide deposit and intracauldron deposits of the Mine Sequence, Noranda, Quebec

5.2 billion. The Horne mine was also a company builder. After optioning the property from Ed Horne (Tremoy Syndicate) in 1922, the Thomson-Chadbourne Syndicate discovered the deposit in 1923 and quickly grew to become Noranda, one of the world’s premier mining companies. This discovery fuelled exploration and, along with subsequent discoveries in the Val d’Or-Cadillac camps, led to the “economic development” of northwestern Quebec. The Horne deposit influenced and continues to influence genetic models for volcanogenic massive sulfide (VMS) deposits. Early observations at Horne contributed to an epigenetic replacement theory for VMS deposits. The most recent genetic model for the Horne, invoking sub-seafloor sulfide replacement of silicified and sericitized volcaniclastic host rocks within a graben, has subsequently been proposed for another giant VMS deposit, the Kidd Creek mine. The Horne and Kidd Creek deposits show many similarities, such as localization within synvolcanic grabens, long-lived hydrothermal activity uninterrupted by volcanism, sub-seafloor replacement sulfides, stacked sulfide lenses, zone refining, silicified footwall rocks characterized by high positive δ18O values, and association with FIII rhyolites. Notable differences between the two deposits include the lack of andesitic, basaltic or komatiitic flows at Horne, different inferred water depths, high Au content at Horne versus negligible Au, but sub-economic to economic concentrations of Sn, In and Cd at Kidd Creek.