GEOLOGY AND MINERAL RESOURCES OF THE ORTIZ MINE GRANT, SANTA FE COUNTY, NEW MEXICO Open-file Report 560 By Stephen R. Maynard Consulting Geologist 1503 Central Ave., NW, Suite A Albuquerque, NM 87104 New Mexico Bureau Geology & Mineral Resources New Mexico Institute of Mining & Technology Socorro, New Mexico 87801 March 2014 ABSTRACT The Ortiz Mine Grant, as defined by a patent issued by the US Congress in 1861, forms an approximately 10 mi x 10 mi tract centered on the old Ortiz Mine in the eastern part of the Ortiz Mountain range in the southwestern part of Santa Fe County, New Mexico. The Ortiz Mountains, physiographically and geologically, form part of a north-south trending mountain range known as the Ortiz Porphyry Belt that includes, from north to south, the Cerrillos Hills, the Ortiz Mountains, the San Pedro Mountains, and South Mountain. Proterozoic basement rocks, consisting of amphibolite schist and quartzite, crop out in the southern part of the Little Tuerto Hills, in the southwestern part of the Ortiz Mine Grant. These rocks are similar to those exposed in the Monte Largo Hills, about 8 km (5 mi) to the south, and are believed to be approximately 1.6 billion years old. Mississippian through Permian rocks are exposed in the northern part of the Little Tuerto Hills, in the San Pedro Mountains (on the Grant’s southern margin), and on low ridges and in arroyo exposures in the area of Tuerto Arroyo, south of the Ortiz Mountains. Paleozoic rocks cumulative thickness is estimated at 745 m (2,450 ft). Although somewhat obscured by faulting, intrusions of younger sills and stocks, and thermal metamorphism, there is a nearly complete section of Mesozoic rocks exposed in the Ortiz Mountains. Total thickness of the Mesozoic section measures about 2590 m (8515 ft). The Paleocene Diamond Tail Fm and the Eocene Galisteo Fm. were deposited in a tectonic basin (the Galisteo Basin) that appears to have been controlled by Laramide movement on the Tijeras-Cañoncito Fault System (TCFS). More than 450 m (1500 ft) of the Paleocene Diamond Tail Formation is preserved in the Ortiz Graben. The Diamond Tail Fm is thickest in the Ortiz Graben, suggesting that the deepest part of the basin during the Paleocene lay in the Ortiz Mountains. Igneous rocks on the Ortiz Mine Grant may be divided into an early calc-alkaline phase and a later slightly alkaline phase. The calc-alkaline phase is represented by extensive laccolithic intrusions of andesite porphyry that have been dated by 40Ar/39Ar at 34.29 – 35.79 Ma. The laccolithic intrusions occur at all stratigraphic levels. The alkaline phase is represented by stocks and dikes including augite monzonite, latite porphyry, and trachytic latite with 40Ar/39Ar ages ranging from 33.27 Ma to 31.68 Ma. Volcanism associated with the igneous activity in the Ortiz Mountains is represented by the Dolores Gulch vent breccia or diatreme. Lavas and pyroclastic deposits of the Espinaso Fm are present only in the northeastern corner of the Grant; these represent the distal facies of volcanoes centered in the Ortiz Mountains, such as the Dolores Gulch vent, and others centered in the Cerrillos Hills and San Pedro Mountains . 40Ar/39Ar ages of the Dolores Gulch volcanic are 31.31 to 31.48 Ma, and thus correlate with the alkaline phase. The major feature of the TCFS in the Ortiz Mountains, the Ortiz Graben, cuts the 34.29 – 35.79 Ma laccolithic intrusions, and is cut by the 33.27 Ma augite monzonite, the constraining its formation to a roughly 1 million-year period from 34.29 to 33.27 Ma. Mid-Tertiary movement resulted in left-lateral, down-to-the-north movement across the TCFS. Mineralization in the Ortiz Mountains is mostly located along or adjacent to strands of the TCFS. Mineralization styles include skarn Au-Cu at Lukas Canyon and the Iron “Vein” prospect, open-space breccia fillings associated with a collapse breccia pipe at Carache Canyon and along margins of the Dolores Gulch volcanic vent or diatreme at the Cunningham Hill mine and Florencio prospect, veins at the old Ortiz and Candelaria mines, and porphyry Cu-Au mineralization in upper Cunningham Gulch. Cross cutting relations at Carache Canyon suggest that the 31.56 – 32.20 Ma 40Ar/39Ar range of ages of adularia is the age of mineralization. This age is taken to be representative of all metallic mineralization in the Ortiz Mountains. The Old Placers Mining District refers to placer and lode mineral deposits found in the Ortiz Mountains and its surroundings. Placer gold was discovered in Dolores Gulch, in the eastern part of the Ortiz Mountains, in the early 1820s. Lode deposits began to be developed by 1830. From the 1820s to the present (2014), artisanal prospecting, mineral exploration, and mining have resulted in the identification of several mineral prospects, identification of mineral resources at Lukas Canyon and Carache Canyon, and the extraction of 250,000 troy ounces of gold and about 50,000 troy ounces of gold at the Cunningham Hill and Old Ortiz Mines, respectively. The old Ortiz Mine, on the northwest side of the Dolores vent breccia, was the original lode discovery in the area and is estimated to have produced about 50,000 troy ounces of gold at intervals from the late 1820s to the 1930s. The mine exploited a narrow magnetite/pyrite-filled fissure on 8 levels over 350 ft total depth. At the Cunningham Hill mine gold and tungsten mineralization is hosted by open-space breccia formed principally in quartzite formed in sandstone of the Diamond Tail Fm immediately adjacent to a pyritic latite porphyry dike, and, to a lesser extent, in the Dolores Gulch volcanics. Gold occurs as fine, rarely visible, grains in fractures in pyrite. Tungsten occurs in scheelite in open spaces, along with pyrite, magnetite, hematite, and calcite gangue. The Cunningham Hill Mine operated from 1979 to 1987 and produced approximately 250,000 troy ounces of gold from 6 million short tons grading 0.055 oz/st. Tungsten was not recovered. About 12 million short tons of rock were removed as overburden or waste. Gold was extracted from the crushed ore by a cyanide leach - activated carbon adsorption - electroplating process. Gold mineralization at Carache Canyon, outlined by an exploration campaign in the 1980s to early 1990s, occurs as coarse, commonly visible, grains with a gangue of pyrite, pyrrhotite, carbonate minerals, and lesser arsenopyrite, chalcopyrite, and sphalerite in open-space fractures along and outside of the southern and western margins of a collapse breccia pipe. Subsidence within the breccia pipe is estimated to be 120 to 240 m (400 to 800 ft). The open spaces are best preserved in andesite porphyry sills and the Point Lookout sandstone, resulting in a series of “stacked” mineralized bodies separated by lower-grade Menefee and Upper Mancos shales. A total resource of 1,169,000 troy ounces of gold contained in 16.7 million short tons at an average grade of 0.07 oz/st was published for Carache Canyon in 1991. The gold-copper-bearing garnet-pyroxene skarn-altered Greenhorn limestone bed forms an east-dipping slope in the upper part of Lukas Canyon in the southwestern part of the Ortiz Mountains. Resources of 180,000 troy ounces of gold and 15,000 short tons of copper contained in 5.44 million short tons grading 0.03 oz/st gold and 0.25% copper were published in 1991. TABLE OF CONTENTS……….…………..……………………………………….i LIST OF FIGURES…………………………………………………………………vi LIST OF TABLES…………………………………………………………………...x INTRODUCTION………………………………………………………………....…1 LOCATION AND HISTORY………………………………………………….…1 PURPOSE……………...…………………………………………………….……1 PREVIOUS WORK……………………………………………………………….4 GEOGRAPHIC SETTING………………………………………………………..6 Physiography……………………………………………………………....6 Climate………………………………………………………………...…11 Vegetation and wildlife……………………………………………….….11 Land use……………………………………………………………….…12 ACKNOWLEDGEMENTS…………….………………………………………..12 SEDIMENTARY ROCKS…………………………………………..……………14 PRECAMBRIAN METAMORPHIC ROCKS………………………………….14 Amphibolite schist…………………………………………………….…14 Quartzite……………………………………………………………….....14 PALEOZOIC SEDIMENTARY ROCKS……………………………………….19 MISSISSIPPIAN SYSTEM……………………………………………..19 Del Padre (?) Sandstone (Arroyo Peñasco Group)………………19 PENNSYLVANIAN SYSTEM………………………………………….19 Sandia Formation………………………………………………...19 Madera Formation………………………………………………..19 PERMIAN SYSTEM……………………………………………...……..19 Abo Formation…………………………………………………...20 Yeso Formation……………………………………………….….20 Glorieta Sandstone……………………………………………….20 San Andres Formation…………………………………………...20 MESOZOIC SEDIMENTARY ROCKS……………………………………...…21 TRIASSIC SYSTEM……………………………………………….……21 Moenkopi Formation………………………………………….…21 Chinle Group…………………………………………………….21 Agua Zarca Formation…………………………………...21 Chinle Group, undifferentiated………………………….21 JURASSIC SYSTEM……………………………………………………22 San Rafael Group…………………………………………….…..22 Entrada Sandstone……………………………………….22 Todilto Formation………………………………….…….22 Summerville Formation……………………………….…22 Morrison Formation………………………………………….…..22 i CRETACEOUS SYSTEM…………………………………..……….….25 Dakota Formation………………………………………….….…25 Mancos Shale…………………………………………………....26 Graneros Shale Member……………………………..…..26 Greenhorn Limestone Member………………………..…26 Carlile Shale Member……………………………….…...28 Juana López Member………………………………….....28 Niobrara Shale Member……………………………….....29 Hosta-Dalton Sandstone (Mesa Verde Group)…………….….…29 Upper Mancos Shale Member……………………….…..29 Mesa Verde Group…………………………………………….…32 Point Lookout Sandstone…………………………….…..32 Menefee Formation………………………………………32 Lower Menefee Member…………………………34 Harmon Sandstone