GeOCHemISTea

• The mineralogy hidden in your assays with Scott Halley

  This month on GeOCHemISTea, Sam sits down with Scott Halley to talk about extracting meaningful mineralogy from standard four-acid assay data. Scott walks through how the classic MINSQ approach evolved into modern linear-programming methods that handle solid solutions, honor thermodynamics, and produce fast, first-pass mineralogy models.They also dig into ambiguity in geologic interpretation, “cognitive entrenchment” in porphyry systems, and how linking calculated mineralogy to rock physics is helping bridge the gap between geochemistry and geophysics.For this episode we read: MINSQ - a least squares spreadsheet method for calculating mineral proportions from whole rock major element analyses (Herrmann and Berry, 2002)

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• Geochemistry Without Borders: A Conversation with Alecos Demetriades

  Alecos Demetriades, applied geochemist and Chair of the IUGS Commission on Global Geochemical Baselines (2024–2028), joins GeOCHemISTea to unpack the Global Geochemical Reference Network (GGRN): why a 160×160 km grid matters, how harmonized sampling/analysis underpins trustworthy baselines, and what QA/QC must look like before interpretation. We touch on FOREGS, leveling national datasets to global references, and practical ways exploration and mining teams can access, use, and contribute to these datasets. Plus: tea stories during Tea Time and why passing knowledge to the next generation keeps this global effort moving. For this episode we read: ⁠International Union of Geological Sciences Manual of Standard Methods for Establishing the Global Geochemical Reference Network⁠  

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• Geochemical exploration in low sulfidation epithermal systems with Simon Griffiths

  This month on GeOCHemISTea, we welcome back Simon Griffiths, Principal Consultant at Third Planet Exploration Services, to unpack the geochemical exploration strategies for low-sulfidation epithermal systems. From vein textures to vanadium-rich roscoelite halos, Simon walks us through practical strategies for geochemical targeting and alteration mapping. He shares insights into sampling, spectral workflows, and how roscoelite at Porgera became one of the most reliable vectors to high-grade gold. Plus a wild tale about how an ICP machine was used to crack down on gold theft in the mine lab. For this episode we read:Geology of the Porgera Gold Deposit, Papua New Guinea (Hay et al., 2020) 

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• From Sardis to the lab: a gold assay deep dive with Hugh De Souza

  In this episode of GeOCHemISTea, we're joined by Hugh De Souza to explore the evolution of gold analysis; from 4,000-year-old fire assay traditions to disruptive technologies like photon assay. With over 40 years at research and industry analytical labs and deep experience in mineralogy, geochemistry, and lab innovation, Hugh shares his unconventional path into analytical geochemistry, breaks down the physics behind modern methods, and reflects on what the future holds for gold assay. Whether you're a field geo or into analytical chemistry, this one's for you.

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• Fine Fractions & Big Discoveries: A Deep Dive into Drainage Geochem with Mary Doherty

  This month on GeOCHemISTea, we are talking about one of exploration geochemistry’s most foundational, and rapidly evolving, methods: stream sediment sampling. Sam is joined by geochemical consultant and educator Mary Doherty, lead author of a 2023 review on stream sediment geochemistry, published in Geochemistry: Exploration, Environment, Analysis.Mary shares a career’s worth of field, lab, and leadership experience, from carrying samples for her USGS geologist father as a child to building geochem training programs for Newmont and ALS, and recently teaching at the Colorado School of Mines. We talk about key developments in stream sediment methods, from fine fraction and BLEG to HMC and indicator mineral chemistry, as well as how to choose the right tool for the job.The episode also covers the practicalities of QA/QC, field planning, and how geomorphology and hydrology shape interpretation. Mary emphasizes the importance of training, knowledge-sharing, and the growing integration of mineralogical data, and machine learning into modern workflows.Whether you are designing your first drainage survey or revisiting legacy data, this episode is a reminder that good geochemistry begins with solid fundamentals and that the future of exploration is already here.For this episode we read: Stream sediment geochemistry in mineral exploration: a review of fine-fraction, clay-fraction, bulk leach gold, heavy mineral concentrate and indicator mineral chemistry (Doherty et al., 2023)

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