Great Plains Margin (Alkaline-related) Mineral Deposits in New Mexico: Twenty Years Later

摘要

The North American Cordilleran alkaline-igneous belt extends from Alaska and British Columbia southward into New Mexico and eastern Mexico. Along this belt, gold, fluorine, zirconium, rare earth elements (REE), and other elements have been found and exploited from several types of mineral deposits. In New Mexico, the belt extends from the Sangre de Cristo Mountains, southward to the Cornudas Mountains, in the northern Trans-Pecos alkaline belt. North and McLemore (1986) and McLemore (1996) summarized the deposits in this belt and called them Great Plains Margin (GPM) deposits. Significant gold production in New Mexico has come from deposits found within this belt. The New Mexico deposits also have been referred to as Au-Ag-Te veins, Th-REE veins, alkaline-igneous related gold deposits, porphyry gold deposits, and Rocky Mountain Gold Province. Since 1996, only minor exploration and development of these deposits occurred because of low commodity prices and environmental concerns. However, as the current demand for critical commodities like REE and tellurium has increased, new exploration programs have encouraged additional research on the geology of these deposits. The origin of these deposits is still not well understood, but compilation of new and past data, including new geologic mapping, age dates, and isotopic and chemical analyses of igneous rocks and associated mineral deposits, allows for a better understanding of the characterization and origin of these deposits. GPM deposits consist of six primary deposit types: (1) polymetallic epithermal/ mesothermal veins, (2) gold-bearing breccias/quartz veins (±tellurium), (3) copper-gold/gold porphyries, (4) copper, lead/zinc, and gold skarns and carbonate-hosted deposits, (5) iron skarns and replacement bodies, and (6) Th-REE epithermal veins. Gold placer deposits derived from alkaline intrusive sources are a seventh deposit type. GPM deposits have high gold/silver and gold/base-metal ratios, unlike other deposits in the state. Deposits of REE are found in several districts, but typically do not contain significant gold, although trace amounts of gold are found locally. Zoning in GPM deposits is common in many districts. The diversity of igneous rocks and associated mineral deposits along the boundary of the Great Plains with the Southern Rocky Mountain and Basin and Range provinces suggests that this region is characterized by highly fractionated and differentiated, multiple pulses of magmas. Both upper mantle and lower crustal source rocks may be involved. Deep-seated fracture systems or crustal lineaments apparently channeled the magmas and hydrothermal fluids. Once magmas and metal-rich fluids reached shallow levels, the distribution and style of these intrusions, as well as the resulting associated mineral deposits were controlled by local structures and host wall rock compositions. Santa Fe Gold Corporation is pursuing potential development in the Old Placers district, where the Carache Canyon breccia deposit is estimated to contain 11.7 million metric tons of 1.6 ppm Au and the Lukas Canyon skarn deposit is estimated to contain 13 million metric tons of 0.9 ppm Au. Other districts have potential for gold including the Jicarilla Mountains, White Oaks, and Orogrande districts. There is REE potential in the Laughlin Peak, Gallinas Mountains, and Cornudas Mountains districts and exploration, including drilling, continues in the Gallinas and Cornudas Mountains. The Organ Mountains and Nogal-Bonito districts have tellurium potential as well.