Genesis of Topaz in Rhyolite Domes | Topaz Mountain Case Study

The gemstone mineral topaz forms in a variety of genetic environments. In this project, we explore the rhyolite-topaz deposit type through a case study on the Thomas Range in Juab County, Utah.

Applying principles of prospecting, we’ll investigate topaz formation in volcanic vents throughout a lava dome in the Cove of Topaz Mountain. You can expect to learn about western Utah's geologic history, lava dome anatomy, geochemistry, crystallization kinetics, thermoluminescence, colour-change reactions, and how to track productive vents to pockets lined with topaz.

Video chapters:
0:00 Introduction
0:30 Project Overview
1:03 Geologic History of the Thomas Range
2:11 Lithologies of Topaz Mountain
4:17 Volcanic Vents
5:24 Route Planning
6:44 Mining Claims
7:53 Day 1: Prospecting (Field)
14:06 Day 2: Prospecting (Field)
20:00 Day 3: Prospecting (Field)
20:25 Vent Identification (Field)
25:33 A Productive Vent (Field)
28:12 Day 4: Vent Hopping (Field)
31:24 How Topaz Forms in Rhyolite
34:09 Structural Controls of Deposits
36:38 Secondary Minerals
37:46 Thermoluminescence
38:54 Photosensitivity Experiment
40:11 Inclusions
41:29 Crystal Morphology
43:01 Tips for Collecting

Pitstop on I-70 in Utah for roadcut minerals and fossils
Coordinates: 38.93380, -110.35140 (Datum: WGS84)


Mineral Resources and References:
Mobile app I use for prospecting and mapping mineral deposits: Gaia GPS
Affiliate link (10% off subscription): https://alnk.to/eDT98T4

Other great videos at the Cove of Topaz Mountain:
Bryan Major:    / @thecrystalcollector  
Nico Jackson:   / nicojax  
Frank & Kyndall:    / thatcampingcouple  
The Rugged Rockhound:    / @theruggedrockhound  
Guided prospecting tours in the Thomas Range offered by Topaz Mountain Adventures: https://topazmountainadventures.com/


Geologic Map and Cross-Sections of Tertiary Rocks in the Thomas Range and Northern Drum Mountains, Juab County, Utah
Download the map: https://ngmdb.usgs.gov/Prodesc/prodde...

The Cove (mineral data): https://www.mindat.org/loc-8742.html
The Cove (BLM info): https://www.blm.gov/visit/topaz-mountain
Book: Holfert, John., Mroch, Walter. (1996). A Field Guide to Topaz and Associated minerals of the Thomas Range, Utah. Volume I. HM Publishing.
Book: Hoover, D. B. (1992). Topaz. Butterworth-Heinemann Gem Books.


This project is designed to be a complete guide to topaz formation in a rhyolitic setting. The Cove is but one of many of these settings. With a little research, I have prepared a list of other localities with similar volatile-rich rhyolite that are worth investigating for topaz.

United States:
-Ruby Mountain, Colorado
-Thomas Range (northern areas), Utah
-Wah Wah Mountains, Utah
-Pine Canyon Caldera, Utah
-Black Range, New Mexico
-Sierra Blanca, Texas
-Del Norte County, California

Mexico
-Zacatecas and San Luis Potosi
Spain
-Cerro de San Cristobal, Galicia
Russia
-Ilmen Mountains, Urals
Japan
-Tamagawa, Akita Prefecture
Australia
-Mount Surprise, Queensland


Crystal Giveaway Winners:
🎉Summer Solstice Giveaway 1: @brennanrobinson6640
🎉Autumn Equinox Giveaway 2: @AveryWalema
🎉Autumn Equinox Giveaway 3: @ianbart2094