Monday, 9 February, 2026/Edition 97

Have you ever been to a mineral, rock, or fossil show? These expos are a paradise for geologists. The 71st Tucson Gem & Minerals Show—“the largest, oldest, and most prestigious gem and mineral show in the world”—will be held February 12–15 in its namesake city.

Additionally, this month, there are mineral shows in Utah (where I live), California, Colorado, Texas, and some other places. As a nod to these events, this week we will focus on mineralization.

Rasoul Sorkhabi

Editor, Core Elements

Metallogenic Processes of East Tethyan Tectonics

Natalia Kirsanova/Shutterstock.com

Porphyry copper deposits (PCDs) are major global sources of copper, gold, molybdenum, silver, lead, zinc, palladium, tungsten, and other metals.

• These deposits may be categorized as “fertile” or “barren” depending on their tectonic and magmatic controls.

The Tethyan orogenic belt resulted from the subduction of the Tethys Ocean beneath Eurasia and the subsequent continental collision of the African, Arabian, and Indian plates with Eurasia.

• This vast northwest-southeast trending belt may be divided into western (European), central (Turkey and Iran), and eastern (Pakistan-India-Tibet) segments.  

• The region is rich in mineral deposits formed during the following tectonic stages:

  •  Pre-collisional (ocean subduction),

  • Syn-collisional (thin continental crust)

  • Post-collisional (thickened continental crust)

Several recent studies in the eastern Tethyan segment shed light on these different mineralization stages. Let’s take a look.

Study #1. Tectonic Controls on Metallogenesis in Pakistan and Tibet

A study by Pakistani and Chinese geologists published in 

International Geology Review discusses tectonic and metallogenic processes in three key areas in the eastern Tethyan domain.

No. 1: Gandese magmatic rocks in southern Tibet

• Twelve Gandese PCDs are located between longitudes 89 and 92 degrees East.

• These deposits are associated mainly with post-collisional Oligocene and Miocene igneous rocks.

• These adakite-like porphyry intrusions originated from partial melting of thickened mafic lower crust, probably related to asthenospheric rise and high fluid input.

• The rocks exhibit high oxidation states (delta FMQ larger than 1) and high Sr/Y and La/Yn ratios.

No. 2: Kohistan Arc in Pakistan

• Samples from Mirkhani-Drosh granodiorite-diorite intrusions exhibit intra-oceanic island arc porphyry mineralization.

• The rocks formed during the Cretaceous.

• Metamorphic dehydration and high-pressure differentiation under garnet stability caused sulfide and volatile loss and resulted in limited ore fertility.

No. 3: Chagai in Pakistan

• The Chagai porphyry region, to the west of the Chaman transform fault, provides a multi-phase tectonic and magmatic evolution resulting in ore fertility.

• It began as a juvenile arc containing tholeiitic basalt and andesite in the Late Cretaceous, transitioned to calc-alkaline thick batholith intrusion during the Eocene, and was finally affected by younger volcanism during Pliocene-Pleistocene times.

• At least five mineralization events resulted from the multi-phase tectonic evolution.

Why it matters: Integrated geochemical-tectonic analyses and comparative case studies reveal the important roles of crustal thickness, subduction-related fluids, and tectonic settings in ore fertility in igneous rocks.

Studies #2 and #3. Post-collisional Porphyry Copper Mineralization in Yunnan, China

Why they matter: These two case studies highlight important variations in PCDs within the same igneous belt resulting from localized tectonic and magmatic conditions.

The first study, published in the GSA Bulletin, compares two post-collisional igneous intrusions in the Ailaoshan-Red River porphyry belt in Yunnan, China.

What researchers found:

• U-Pb zircon ages show that the Machangqing and Songgui intrusions are 35 Ma.

• The Songgui intrusion is PCD barren, while the Machangqing intrusion is PCD rich.

• The researchers attribute the PCD fertility in the Machangqing intrusion to coeval mantle-derived ultrapotassic melts.

Another geochemical study of porphyry intrusions in the Ailaoshan-Red River region, published in Ore Geology Reviews, reports that:

• The 34-Ma Yao’an intrusion within the Jurassic-Cretaceous sediments is not a typical porphyry system but a hydrothermal vein type.

• The Yao’an intrusion lies about 50 kilometers to the southeast of the Machangqing intrusion.

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Mantle Processes Control Ore Deposits in Southern Australia

Hiltaba Pink Granite/Piccader/Wikimedia Commons

In Nature Scientific Reports, Stephen Thiel and colleagues present an interesting study of the Mesoproterozoic iron-oxide-copper-gold (IOCG) deposits in the Gawler Craton in southern Australia controlled by mantle-derived fluids.

Study area:

• The Gawler Craton consists of two major lithospheric blocks: eastern and western. The eastern block contains metamorphic rocks of 1790–1640 Ma, and the western block contains weakly metamorphosed rocks of 1730–1690 Ma.

• Both blocks experienced lower crustal melting and intrusions at 1590 Ma.

• The central part of Gawler Craton experienced massive volcanism at 1590 Ma.

• Seismic tomography shows the lithosphere-asthenosphere boundary to be as deep as 220 kilometers in the central volcanic part of the Gawler Craton.

• The Olympic Copper-Gold Province is the junction between the western and eastern blocks.

3-D resistivity model:

• The researcher constructed a 3-D resistivity model of the lithosphere beneath the Gawler Craton.

• The data came from the Australian Lithospheric Architecture Magnetotelluric Project.

• The model shows that crustal depths of 20–100 kilometers exhibit highly resistive (greater than 10,000 ohm-meter) in the central Gawler Craton beneath the 1.59-billion-year-old Gawler Igneous Province.

• This central resistivity region is surrounded by a vast arcuate-shaped low resistivity zone at depths of 10–80 kilometers.

• The conductor (low resistivity) region is the main locus of copper mineral deposits.

Two-stage tectonics: It seems that the enrichment of copper and iron in the Gawler IOGC deposits is related to two tectonic events:

1. 1620 Ma: This event involved subduction-related metasomatism and led to enrichment of the bottom of the lithospheric mantle. The northeast-southwest conductor lineament corresponds to the subduction zone, accompanied by a linear back arc.

2. 1590 Ma: The second event caused significant tectonic re-mobilization and widespread magmatic emplacement. This event transported metal-rich magmas to the surface and caused hydrothermal alterations.

Why it matters:

• Mineral exploration usually focuses on surface mapping and geochemical analysis of ore deposits.

• This case study from southern Australia shows how geophysical modeling of subcrustal mantle architecture and fluid plumbing systems reveals deep-seated controls on ore mineralization.

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