GOETHITE AFTER SIDERITE: THE PRESENCE OF GOETHITE AFTER SIDERITE PSEUDOMORPHS IN A PEGMATIC MATRIX FROM LAKE GEORGE, COLORADO

Samples containing goethite after siderite pseudomorphs, inside of a pegmatite matrix, have been collected from Goethite Mountain, Colorado. One sample collected contains numerous well-formed goethite pseudomorphs after siderite that are 0.5 to 3.5 centimeters across. These euhederal crystals appear to have formed in open pockets in a highly brecciated, miarolitic pegmatite. The least brecciated part of the rock is composed of graphic granite, with interlaying clear, and smoky quartz, along with feldspar. The minerals identified in hand sample vary from euhederal to anhederal, with the goethite pseudomorphs showing a box-work pattern. The sample contains three distinct regions within: one of a brecciated goethite pseudomorphs matrix, one comprised of a brecciated NYF-enriched pegmatite, and one of the low-brecciated graphic granite. The mineralogical composition of the rock changes through these regions, with the graphic granite containing higher abundances of feldspar, and with the pegmatite containing higher volumes of quartz and a different variety of feldspar from the other regions. The sample has also weathered at different rates, with some areas goethite weathering into yellow ochre, and other areas containing metalliferous luster. The location of Colorado where this sample was obtained is known for the Pikes Peak batholith, which produced a miarolitic pegmatite, and shows a complex history of formation.