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Iron oxide copper-gold (IOCG) systems have become important worldwide exploration targets. Some of the largest mineral deposits in the world are classified as IOCGs. Examples include the huge Olympic Dam and Ernest Henry deposits in Australia and the Kiruna district in Sweden.
Ore deposits with IOCG affinities occur in a variety of geological settings around the world with a significant number identified in Paleoproterozoic terranes. Typically IOCG districts are associated with regional scale magnetite-hematite bearing alteration systems. Economic mineralization is generally associated with late stage epithermal events. IOCG deposits are frequently associated with intracratonic rifts. The Salobo and Igarape Bahia deposits, located in the Carajas Mineral Province, Brazil and the Clonclurry District in Australila are three of the best known rift-related IOCG examples and have geological settings which are similar to the setting of the Wilson Creek area.
In North America, the Midcontinent Rift-related terranes have many geological similarities to other areas elsewhere in the globe that host IOCG deposits. In the Upper Peninsula of Michigan (UP), Prime Meridian has identified a geological terrane with characteristics favorable for the formation of IOCG deposits.
The geological framwork of the UP is dominated by intrusive, volcanic and sedimentary rocks fo the Early to Mid-Proterozoic Marquette Range Supergroup. The Supergroup is characterized by a thick sequence of platformal clastic and chemical metasedimentary rock, with subordinate bimodal metavolcanic rocks. This terrane is distinguished by the presence of major oxide facies (superior type) iron formation. the supracrustal assemblage was deposited on an Archean basement, intruded by ultramafic to granitic intrusions and deformed and metamorphosed during the Penokean Orogeny. A post penokean period of Alkaline intrusive emplacement is evident in the region. Studies by the USGS have also shown that the terrain has been affected by a Post-Penokean (Yavapi) thermal event.
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Regional Geology Compiled by PK Simms 1992 | A late Proterozoic (Keweenawan) extensional period of Intra-cratonic rifting, now centered on Lake Superior, split the Supergroup assemblage apart.
In this area, Prime Meridian has identified a geological terrane with the characterisitics favorable for the formation of IOCG deposits.
Regional Geology
In North America, the Midcontinent Rift-related terranes have many geological similarities to other areas elsewhere in the globe that host IOCG deposits. In the Upper Peninsula of Michigan (UP), Prime Meridian has identified a geological terrane with characteristics favorable for the formation of IOCG deposits.
Wilson Creek
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Aeromagnetic Image of the Wilson Creek Project Area |
Geological mapping and prospecting by Prime Meridian has identified metallic mineralization and alteration of characteristic of other IOCG deposits elsewhere in the globe.
The Wilson Creek Project Area is located in one of a series of four structural domes formed during the Penokean Orogeny in the central UP. The domes are characterized by a magnetically quiet center and a strongly magnetic rims (iron formation and metavolcanic rocks) that are set in a magnetically quiet background of the Michigamme Formation.
The Wilson Creek Dome was the focus of Prime Meridian's exploration because of an unusual disruption in a rimming positive magnetic anomaly at its south end. The positive magnetic signature is disrupted by a strong linear magnetic low trending roughly northeast-southwest. This low is interpreted to be the result of magnetite destruction during a hydrothermal mineralizing event.
Within this trend Prime Meridian discovered copper + gold + tungsten + molybdenum mineralization in hydrothermally altered metavolcanic rocks in float. Grab samples returned assays up to 2.6% copper, 0.22 parts per million gold and 0.13% tungsten.
Altered Boulders in the Epidote Field | |
These boulders are exposed in a clear cut in the Project Area, informally referred to as the Epidote Field. The float boulders are large and angular. At the western end of the clear cut, the boulders are compositionally homogenous and dominated by hydrothermally altered basalt. Geological mapping suggest that the rocks may have undergone an early sodic-calcic epidote alteration which was overprinted by a later potassic-hematitic (quartz + Kspar + Biotite + hematite) alteration. The observed copper +/- , tungsten+/- molybdenum +/- gold mineralization is generally associated with the late alteration. However chalcopyrite mineralization also occurs disseminated and in rare veinlets associated to a lesser degree with the earlier epidote alteration assemblage.
The angular and homolithic nature of the boulders suggests that they may not have moved far from their source. Prime Meridian is mapping the Pleistocene geology of the area to determine the source of these boulders.
Wilson Creek Discovery Boulder
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IOCG Style Mineralization
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Chalcopyrite Mineralization
in Discovery Boulder
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Second Altered and Mineralized Boulder
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Alteration Paragenisis at
the Wilson Creek Project Area
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Chalcopyrite Mineralization WC-2
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In 2007, Prime Meridian drilled 3 core holes in this area. Secondary chalcopyrite mineralization was intersected in DDH WC-2. The chalcopyrite consisted of thin intervals crosscutting 5--10 cm thick veins of massive chalcopyrite with secondary hematite, k-spar, biotite, chlorite, fluorite and tourmaline. The best assay recovered from the core was 1.53% Cu across 0.6 meters with trace amounts of gold, silver, and fluorine.
A program of limited wide space soil sampling returned results that supported PMR's theory for the source of the mineralized boulders. The target area correlates with the zone of magnetic disruption and PMR has designed an exploration program to test this very prospective target. In addition to the targets in the Wilson Creeek area, PMR has also identified several other IOCG targets in the UP for follow up. Research by PMR indicates that the IOCG targets discovered by PMR indicates that the IOCG targets discovered by PMR may be part of a larger, previously undefined, IOCG district with Michigan's Upper Peninsula.
Prime Meridian also completed a ground magnetometer survey of on the Burns prospect, a discrete airborne EM and positive magnetic anomaly which is located 2 kilometers south of the Epidote Field and adjacent to the southward extension of the magnetite destruction zone. Ground HLEM and magnetometer surveys have confirmed the presence of a coincident Magnetic and EM anomaly. This project is drill ready.
Ground Magentic Survey at the Burns Prospect
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