The Portuguese Creek Claim Area
Portuguese Creek is a part of a much larger geological feature known as the Magic Reservoir Eruptive Center (Leeman 1982). The large geological feature is interpreted to be a caldera structure some 125 square miles in surface area, which was filled by the Moonstone Rhyolite in Pliocene time (ca: 5-3 Ma). The Moonstone Rhyolite is subdivided into three units known as the lower, middle and upper Moonstone Rhyolite. The lower and middle units fill the caldera while the upper unit was poured out from points along the ring fracture which bounds the caldera. Those localities where the upper Moonstone Rhyolite occurs at outcrop in some places are marked by elongate structures thought to be volcanic vents. In other locations there is a single volcanic cone from which most of the lava ensued. Petrologically the Moonstone Rhyolite is a hybrid rock, the product of mixing two dissimilar parent magmas, including one that is siliceous (rhyolitic) and the other that is basic (basaltic). The upper unit is the most basic of the three, having the mineral olivine as an essential constituent, which is absent from the lower and middle units.
Portuguese Creek Geology
The property is situated in the southwestern corner of Lincoln County, Idaho. The area is dominated by a conical peak, which rises to a height of approximately 5,908 feet, which is about 300 feet above the neighboring ground. Approximately 2,800 feet away to the southeast is a second smaller conical hill. Both are vents from which issued the mineralized lava flows. These two small volcanoes with their lava fields lie at the headwaters of Portuguese Creek from which the project takes its name.
Nature of Mineralization
The flow rocks are not hydrothermally altered, except for minor deuteric hematization. Because rock alteration is lacking and on the basis of other evidence, in particular a mineralogical study by Bowles (1999), as well as petrogaphic data (Honjo and Leeman 1987), it was tentatively concluded that the mineralization was syngenetic with its host rock. For example, the Bowles study showed that gold was present in the rock as minute films of native metal (up to 20 microns in size) attached to the surfaces of silicate minerals and found evidence for a gold, palladium, tin and aluminum mineral in grains up to 50 microns. The mode of occurrence of the gold and platinum group metals is compatible with the syngenetic hypothesis. As such, this would imply that the Olivine Rhyolite member of the Moonstone Formation to be a very attractive exploration target for gold, palladium and platinum. These two areas were mapped from aerial photographs and indicate that each is about two square miles. The petrology of the Moonstone fit the parameters for mantle plume activity. The release of the 1999 Bowles mineralogical report confirmed the nature of the mineralization as being derived from the earth's deep mantle.