High-grade ores in low-sulfidation epithermal precious metal deposits include banded quartz veins that contain gold dendrites. The processes by which dendrite growth takes place have been subject to debate for decades, especially given that these deposits are known to form from dilute thermal liquids that contain only trace amounts of gold. It is shown here that growth of gold dendrites in epithermal veins at the McLaughlin deposit in California (western USA) originally took place within bands of gel-like noncrystalline silica. The gel provided a framework for the delicate dendrites to form. The high permeability of the gel allowed the diffusion and advection of gold from the thermal liquids flowing across the top of the silica layers to the sites of crystal growth within the gel. Over time, the gel hardened to form opal-AG. This silica phase is thermodynamically unstable and recrystallized to quartz that has a distinct mosaic texture.

Silica sinters forming at the Wairakei geothermal power plant in New Zealand are composed of noncrystalline opal-A that deposited rapidly from cooling geothermal liquids flashed to atmosphere. The sinter is laminated with alternating layers of variably compacted silicified filamentous microbes encased by chains of fused silica microspheres. Microscopic inspection of bonanza quartz vein samples from the Buckskin National low-sulfidation epithermal precious metal deposit in Nevada showed that colloform bands in these veins exhibit relic microsphere textures similar to those observed in the silica sinters from the Wairakei power plant. The textural similarity suggests that the colloform bands were originally composed of noncrystalline opal-A that subsequently recrystallized to quartz. The colloform bands contain dendrites of electrum and naumannite that must have grown in a yielding matrix of silica microspheres deposited at the same time as the ore minerals, implying that the noncrystalline silica exhibited a gel-like behavior. Quartz bands having other textural characteristics in the crustiform veins lack ore minerals. This suggests that ore deposition and the formation of the colloform bands originally composed of compacted microspheres of noncrystalline silica are genetically linked and that ore deposition within the bonanza veins was only episodic. Supersaturation of silica and precious metals leading to the formation of the colloform bands may have occurred in response to transient flashing of the hydrothermal liquids. Flashing of geothermal liquids may thus represent a key mechanism in the formation of bonanza precious metal grades in low-sulfidation epithermal deposits.

Ultramafic rocks are promising candidates for carbon sequestration by enhanced carbon dioxide (CO₂) mineralization strategies due to their highly CO₂-reactive mineral composition and their abundant availability. This study reports the mineralogy and microtextures of a representative ultramafic rock from the Ma-Hin Creek in northern Thailand and provides evidence of CO₂ mineralization occurring through the interaction between CO₂ and the rock in the presence of water under ambient conditions. After sample collection, rock description was determined by optical petrographic analysis. The rock petrography revealed a cumulated wehrlite comprising over 50% olivine and minor amounts of clinopyroxene, plagioclase, and chromian spinel. Approximately 25% of the wehrlite had altered to serpentine and chlorite. A series of CO₂ batch experiments were conducted on six different rock sizes at a temperature of 40 °C and pressure of 1 atm over five consecutive days. The post-experimental products were dried, weighed, and geochemically analyzed to detect changes in mineral species. Experimental results showed that product weight and the presence of calcite increased with reducing grain size. Additionally, the modal mineralogy of the wehrlite theoretically suggests potential CO₂ uptake of up to 53%, which is higher than the average uptake values of mafic rocks. These findings support the rock investigation approach used and the preliminary assessment of carbon mineralization potential, contributing to enhanced rock weathering techniques for CO₂ removal that could be adopted by mining and rock supplier industries.

This work represents a fundamental developing strategy for the self-creation of digital-format geologic maps in the form of mobile apps. The digital geologic maps are apparently more convenient to work with than traditional paper-format geologic maps as the maps are user-interactive, self-directed, and can be easily updated. The digital geologic map mobile apps have recently become significant interactive presentation tools for geology students, geoscientists, and even the public. However, lack of technical methods and software development of those apps have yet revealed. In this study, we provide brief guidelines for database and software development methods to build a geologic map mobile app. The software used in this work is open source. The database file including geological information, spatial relationship and distribution, and a base map of Thailand, was prepared through a geographic information system or GIS. The hybrid app development process, which includes two open-source frameworks, namely Ionic and Angular, is key to produce a mobile app representing geologic maps via mobile devices. Additionally, basic programming language skills such as HTML, CSS, and JavaScript seem to be required for software coding. Following these steps, we produced a mobile app, named DooHin, for displaying a digital geologic map of Thailand with a scale of 1:50000 that is available via the app stores. This app is apparently practical and useful in fieldwork as it encourages a user-interactive experience, general geological information, and a user-positioning system.

Mafic and ultramafic rocks have become a promising approach for atmospheric carbon dioxide (CO₂) reduction, as they are major sources of CO₂-reactive minerals, i.e., olivine, pyroxene, plagioclase, and serpentine. The minerals potentially sequester CO₂ by turning it into a stable solid phase through carbon mineralization in the rock weathering process. However, detailed descriptions and evaluations of the target formations are lacking. This study investigates the mineralogical composition and microtextural characteristics of representative mafic and ultramafic rocks observed in northern Thailand, using a petrographic analysis. The results show that variations in CO₂-reactive mineral assemblages of rocks certainly affect their theoretical CO₂ uptake potential. Ultramafic rocks tend to sequester larger amounts of CO₂ than mafic rocks. The microtextural observation reveals the mineral size ranges of 0.05–5 mm for ultramafic and mafic intrusive rocks and 0.01–2 mm for mafic extrusive and metamorphosed rocks. Reducing the rock size to be equal to the average size of the reactive minerals could be considered one of the practical designs in enhanced rock weathering activities. Understanding the mineralogical and textural characteristics of target rocks thus plays a crucial role in further georesource exploration and engineering designs, supporting climate action strategies on various scales.