January 4th, 2025: This post investigates the cause of crustal-scale electrical conductivity anomalies observed in magnetotelluric (MT) imaging of mineral provinces, specifically in the Olympic Dam region of Australia and the Southeast Missouri Iron Province (SMIP) in the United States and is derived from and a review of Graphite as »
28th December 2024, John C. Menzies: This post is a review of a paper on the impact of mantle oxidation and transport of gold rich fluids from the mantle to the near surface. Overall, this study demonstrates that mantle oxidation by S–bearing aqueous fluids is a key trigger mechanism for »
The atlas has been updated with images from the Onto Deposit in Indonesia courtesy of David Burrows. The Onto deposit currently has an indicated resource of 0.76 billion tonnes (Gt) at 0.93% Cu, 0.56 g/t Au, 5 g/t Ag, and 350 ppm As (7 Mt contained Cu, 13 Moz Au) »
Ben Andrew, Senior Geologist at Mt Isa Mines submitted a captivating PhD thesis (Andrews, B.S., 2020) in 2020 on alteration at Mt Isa and its implications for fluid flow of the hydrothermal fluid that formed the world class Cu and Pb-Zn-Ag orebodies. Here we summarize some of his δ18O results. »
This post is a summary of the excellent recent paper on the above topic in Economic Geology: Jeffrey W. Hedenquist, Antonio Arribas; Exploration Implications of Multiple Formation Environments of Advanced Argillic Minerals. Economic Geology 2022;; 117 (3): 609–643. https://doi.org/10.5382/econgeo.4880 Introduction Hydrothermal ore deposits are associated with alteration minerals, and one such alteration type »
South32 has undertaken a review of the carrying value of the Hermosa Project consisting of the Taylor Zn-Pb-Ag deposit and the Clark Mn deposit. South 32 acquired the Hermosa Project through the all-cash offer for TSX listed Arizona Mining Inc. in August 2018, paying C$6.20 per share. This was a »
The purpose of this post is to delineate the key characteristics of the Mt Isa deposit from an explorer’s pragmatic perspective and then discuss a possible analogue in the Eastern Succession, north of Cloncurry. Beside the fascinating tectonic, geological and structural history of the Mt Isa region, it represents the »
Discovery of the Mt Isa Copper Deposits Silver-lead ore was discovered at Mt Isa in 1923 but it was not until 1927 that a surface drill hole aimed to test silver-lead bodies at depth intersected 15 m of oxide copper and chalcocite grading 17% copper in the Black Rock area. »
The Mount Isa Province in northern Australia is one of the world’s most prospective regions for minerals. It hosts three of the ten largest Zn–Pb deposits in the world, the world-class sediment- hosted Mount Isa copper deposit, and the Ernest Henry IOCG. The Mount Isa copper (225 Mt at 3.3% »
This post is a review and summary of an excellent paper: Bradley Cave, Richard Lilly, Alexander Simpson, Lucy McGee, A revised model for the George Fisher and Hilton Zn-Pb-Ag deposits, NW Queensland: Insights from the geology, age and alteration of the local dolerite dykes, Ore Geology Reviews 154 (2023) 105311. »
Here is an excellent paper from Richard Henley et al that provides support for the argument that potassic alteration is largely isochemcial and and not an introduced component. Henley has elequently defined the porphyry copper environment as that of a dynamic, internally and externally stressed, gas phase reactor where repetitive »
An EGRU conference with a session in honour of Dr Roger Taylor 24 – 28 June 2019 Tinaroo Lake Resort Tinaroo, Atherton Tablelands, tropical north Queensland, Australia The conference will address advances and breakthroughs in understanding the setting, genesis and characteristics of magmatic systems related to Sn-W-Critical Metal mineralisation, including Rare »
Just received the above titled book from Elsevier for review. I had the great pleasure of spending some time in the field in Myanmar with Andrew Mitchell in 2017 and this important contribution by him is a remarkable testament to his life’s work. He has enormous knowledge of the geology »
Dr Roger Taylor is presenting three economic geology short courses in Melbourne in August. Strongly recommended. Field Assessment of Gossans and Leached Cappings, 28th August Coping With Skarns and Their Relationship to Carbonate Replacement Deposits, 29th – 30th August Ore Textures and Breccias, 31st August »
Following the publication of the paper (noted below) on the epithermal portion of the Recsk metallogenic system in Hungary here are 3D models from the entirely concealed Cu-Au mineralized intrusive bodies and related Cu-Au skarns and outbound Zn-Pb replacement bodies. Ore Mineralogy and Fluid Inclusion Constraints on the Temporal and »
This paper in the latest edition of Economic Geology by Ágnes Takács, Ferenc Molnár, Judit Turi, Aberra Mogessie, John C. Menzies examines the evolution of the outcropping epithermal mineralisation at Recsk in Hungary. The epithermal deposit sits close to the apex of a large intrusive body which does not outcrop but was defined by »
Here is a brief paper, by Ralica Sabeva Vassilka Mladenova and Aberra Mogessie on the gold deposits around the small western Bulgarian town of Breznik. We acquired this project for Euromax Resources Limited back in 2003 and we explored this until my departure in 2010. A rather nice intermediate sulphidation gold »
