POTENTIAL FOR LARAMIDE PORPHYRY COPPER DEPOSITS IN SOUTHWESTERN NEW MEXICO AND TRANS-PECOS TEXAS

New Mexico lies at the eastern edge of one of the world’s great metal-bearing provinces, which extends into Arizona, Mexico, and Trans-Pecos Texas, thereby making copper one of NM’s important commodities. More than 14 billion pounds of Cu have been produced from porphyry copper deposits in NM since the early 1800s. Three periods of porphyry copper deposits are found in NM and Texas. The oldest deposits in southwestern NM and Trans-Pecos Texas are 60-75 Ma, exhibit calc-alkaline geochemistry, and include the Copper Flat (Hillsboro, 74 Ma), Eureka (Oro in Little Hatchet Mns, 71.4 Ma) and Red Hills (Texas, 64.2–60.2 Ma) deposits. Exploration and/or permitting are underway in these districts. THEMAX has identified proven and probable reserves of 113 million short tons at 0.30% Cu, 0.009% Mo, 0.096 grams/ton Au, and 1.93 grams/ton Ag at Copper Flat. The next period of porphyry copper deposits in southwestern NM is 50-60 Ma, exhibit calc-alkaline geochemistry, and include the currently producing Chino (58.6 Ma), Tyrone—Little Rock (54.5 Ma), and Cobre (Hanover Mn, 57.55 Ma) deposits. Estimated proven and probable ROM leachable reserves in 2018 at Chino and Cobre are 121 million metric tons of 0.29% Cu; estimated proven and probable millable reserves are 274 million metric tons of 0.54% Cu, 0.04 grams/metric ton Au, 0.93 grams/metric ton Ag, and 0.01% Mo. In 2018, proven leaching reserves at Tyrone are estimated as 55 million metric tons of ore grading 0.25% Cu. Additional deposits formed during this period are in various stages of exploration (Lone Mn, 51.5–50.6 Ma; Lordsburg, 57.3–58.8 Ma). The ages of porphyry copper deposits found at Gold Lake (White Signal), Steins (McGhee Peak), and Mimbres Mns are unknown. The youngest porphyry copper deposits are found in central and eastern NM, are much smaller than Laramide deposits, exhibit alkaline geochemistry, and include the Organ (26-36.45 Ma), Cerrillos (29.8 Ma), and Orogrande (41.4-45.6 Ma) deposits. None of these deposits are active. Other areas in NM have potential for porphyry copper deposits, especially where Laramide polymetallic vein and skarn deposits are found. Numerous geophysical anomalies are found in southwestern NM that could be indicative of additional porphyry copper deposits in the subsurface. Development of these deposits will depend upon the copper market.