Most magmatic Ni-Cu-PGE sulphide deposits occur within long-lived magma pathways fed by high degree partial melts of the mantle. Holistic mineral-system analysis for such deposits has some parallels with dominantly hydrothermal systems, but also some important differences.Major provinces are associated with large volumes of magma erupted at margins of ancient Archaean cratons, and are associated with small intrusions through which large volumes of magmas have passed. There is no demonstrable association with any particular magma type, although in most provinces the ores are found associated with the most primitive available magmas, whatever these may be. Or-bearing intrusions tend to form early in the evolution of the host province, although exceptions exist to this rule, and these intrusions typically account for very small proportions of the volumes of the province as a whole.Ore deposition is favoured by prolonged high-volume flow over a horizontal floor. This floor may take the form of the base of a channelized sill, tube or blade-shaped dyke, which account for most of the known host igneous bodies to significant ore deposits. Deposition mechanisms may be chemical or physical, but large high-grade deposits require a major component of transported sulphide liquid, initially carried as droplets. Late stage migration of sulphide liquid as gravity currents within intrusion networks, coupled with infiltration and melting of floor rocks, accounts for the common observation in mafic intrusion hosted deposits of cross cutting relationships between massive sulphides, host intrusions and country rocks.The following set of criteria is proposed in targeting and evaluating Ni-Cu-PGE sulphide systems: 1) nature of magmatism and relationship to pre-existing cratonic architecture; 2) magmatic and structural controls on the development of protracted-flow magma conduits; 3) access to crustal S A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPTNi-Cu-PGE mineral systems Barnes May 2015 2 sources at some point along the pathway; 4) favorable intrusion geometry and emplacement style for deposition, reworking and upgrading of sulphide magmas, and 5) favorable structural history and erosional level for preservation and detectability.These components can be translated into mappable geological criteria. At the predictive targeting scale, the key features are proximity to ancient cratonic boundaries and long-lived, trans-crustal structures, and relationship to voluminous mafic or ultramafic magmatism typically with high Mg and low Ti contents, but otherwise lacking distinctive characteristics. At the detection scale, there are two distinct approaches: recognition of high volume magma pathways with prolonged flow-through operating at length scales of km based on morphological, petrological, geophysical and structural observations; and identification of the petrographic and geochemical signals of accumulation or extraction of sulphide liquid.

International audienceSerpentinites in a Tertiary subduction complex in the northern Dominican Republic contain low concentrations of incompatible elements in bulk-rock compositions and high Mg in relict silicate minerals. The forsterite component in olivine ranges from 89.0% to 90.8%, and the enstatite component in orthopyroxene ranges from 89.4% to 91.1%, suggesting that they are mantle peridotites. Two different protoliths are identified for the serpentinites based on the bulk-rock compositions and spinel chemistry: abyssal peridotites and forearc mantle peridotites. Hydrated abyssal peridotites are voluminous and occur in ophiolite complexes in the northern terranes (Puerto Plata Complex and the northern part of the Rio San Juan Complex) and in serpentinite mélanges in the central part of the Rio San Juan Complex. The serpentinite mélanges contain fragments of high-pressure–low-temperature rocks and are interpreted to be tectonic mélanges, representing part of a serpentinite subduction channel. The serpentinites show moderate Al/Si weight ratios (0.026–0.081) in bulk rocks and moderate Cr# (atomic ratio of Cr/[Cr + Al] = 0.20–0.55) in spinel. Hydrated forearc mantle peridotites occur along major strike-slip faults, the Camú fault zone, and the Septentrional fault zone. They show low bulk-rock Al/Si weight ratios (up to 0.021), high concentration in Ir-group platinum group elements (13.1–24.6 ppb total), and high Cr# (0.48–0.67) in spinel. Raman spectroscopy and X-ray powder diffraction indicate that lizardite is the predominant serpentine species. The absence of antigorite suggests that these serpentinites were derived from a shallow depth (

Ferritchromite is rarely reported in forearc mantle peridotites. This contribution describes ferritchromite alteration and zoned Cr-spinel in serpentinites from the Rio San Juan Complex in the Dominican Republic. These rocks originated from the forearc mantle and protruded along lithosphere-scale faults in the mid Eocene. # >0.5) is common in ultramafic rocks in amphibolite-grade terranes; however, the serpentinite samples described herein show little evidence of high-grade metamorphism. The lowtemperature serpentine-group mineral lizardite is dominant and high-temperature antigorite is either very rare or absent; other high-temperature minerals, such as talc, tremolite and cummingtonite, are trace constituents. The observed zoning in the Cr-spinel is thought to represent 'immature' ferritchromite, probably formed in response to a short-lived thermal event. This event appears to have been on too short a timescale to produce either proper ferritchromite or significant quantities of high-temperature minerals. It may be related to the emplacement of the nearby Rio Boba Intrusion, or the upward protrusion of the serpentinites along the lithosphere-scale Septentrional fault zone from the base of the mantle wedge through its hotter interior. We suggest that such alteration is rare in forearc serpentinites because they are not commonly heated during exhumation along the plane of subduction. This work demonstrates that Cr-spinel compositions can be modified by relatively low-grade metamorphism.