2021 Speaker Dr. Peter Megaw

The Mineralogy of Mexican Silver Deposits
Dr. Peter Megaw

Mexico has produced 25% of all the silver mined in human history and has over half of the world’s giant silver deposits, so something must be geologically special about Mexico; but what? Few of the ore-forming processes active in Mexico are unique, but her geologic evolution over the last 35 million years created a special combination of size, oxidation, preservation and exposure that is. This special combination puts us at exactly the right moment in geologic time to find her ores and their component primary and secondary mineral species. Understanding more about how and why the major Mexican silver deposits got so big gives collectors a geologic/genetic context for why they are also so specimen rich. This in turn leads to appreciating that minerals from similar deposit types and environments worldwide tend to resemble each other and how being able to decipher the stories told by those resemblances greatly enhances specimen appreciation.


Dr. Peter K.M. Megaw, Is a Consulting Geologist (PhD UofA) President of IMDEX/Cascabel and co-founder of MAG Silver and Minaurum Gold. Peter has been a dedicated mineral collector since first setting foot in Santa Eulalia in 1977. He moved to Tucson in 1979 and quickly joined the Tucson Gem and Mineral Society, taking on the job of Exhibits Chair for the Tucson Show in 1984. This has given him the opportunity to visit most of the world’s major mineral museums with a special eye out for what they should bring to Tucson. His mineral collecting has come to focus almost exclusively on Minerals of Mexico and he has spoken and written extensively on specimen localities there; most recently an in-depth article for Mineralogical Record on the Santa Eulalia Mining District in Chihuahua, Mexico for which he received the Friends of Mineralogy 2018 Award for Best Article in Mineralogical Record. He is also a contributing editor for Rocks and Minerals and occasionally writes for Mineralogical Monographs and Mineral News. In his spare time he collaborates on studies of silver isotopes in silver minerals, is Mindat’s moderator for submissions on Mexico and co-moderator of the FMF Mineral Forum, often with tongue planted firmly in cheek. A combination of the above led him to be awarded the Carnegie Mineralogical Award for 2009.