EXAMINING THE SPATIAL AND TEMPORAL RELATIONSHIPS BETWEEN IGNIMBRITE-RELATED INTRUSIONS THROUGH TIME AND SEDIMENT-HOSTED GOLD OCCURRENCES IN NEVADA

Nevada is one of the world’s largest gold producers. Abundant geochronologic data and geologic mapping indicate that during the accretion of the western US, arc-related magmatism led to much of the State’s precious-metal ore deposits. Beginning around 44 Ma, major ignimbrite eruptions (called the “Ignimbrite Flare-up”) were immediately preceded by emplacement of granitic intrusions into overlain carbonate-rich strata. By examining the location of these intrusions and their proximity to gold occurrences, there may be suitable vectors to locate deposits of economic value.

Analysis of the geochronologic data on igneous rocks show a shift in magmatism through time in Nevada from the northeast at about 44 Ma to the west-southwest after about 15 Ma. However, two time periods, one from 10 to 15 Ma, and the other from 37 to 44 Ma, have more abundant clusters of gold deposits indicating that higher rates of mineralization (or ore deposit preservation) occurred. These age brackets appear to coincide spatially and temporally with the earliest part of the Cascade volcanic chain or arc (~10-15 Ma) and the beginning of Tertiary magmatism in the Eocene (~44-37 Ma). Using Arc tools, the spatial relationship between these igneous intrusions and gold deposits indicate these gold occurrences plotted within 1 kilometer from an intrusive body, suggesting that there is a tight spatial and temporal relationship between the ignimbrite-related intrusion and ore deposition.