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Douglas C. Kreiner

Publications and source records attributed to Douglas C. Kreiner.

3 recordsLinked to original sources

USGS2026

Integrating detrital magnetite geochemistry and (U-Th)/He chronometry as a sediment provenance tool in geologic and metallogenic terranes

Magnetite is ubiquitous in porphyry Cu systems and in sediment sourcing both barren and mineralized regions, with potential as an indicator mineral in concealed and coarsely-mapped terranes. We develop and test a workflow for integrated geochemistry and (U–Th)/He (He) dating for inferring detrital magnetite (DMt) provenance in these settings. The ca. 70 Ma Taurus porphyry Cu–Mo(–Au) district in eastern interior Alaska serves as a test case. DMt from streams draining porphyry-related mineralization was characterized by geochemistry and mineral inclusion and microstructure observations, complemented by similar data for potential porphyry and host rock sources. Principal component analysis and clustering of DMt geochemical data resolve multiple populations in our samples geochemically and texturally compatible with derivation from metamorphic, porphyry-related hydrothermal, and igneous sources. Hydrothermal magnetite comprises ∼16–50% of DMt nearest porphyry mineralization but diminishes to ∼4% ∼15 km downstream. Subsampled grains within populations yield ∼160–110 Ma, ∼70 Ma, ∼55 Ma, and ∼20 Ma magnetite He date modes. Combined with provenance, He dates capture Early Cretaceous regional exhumation of metamorphic host rock and Late Cretaceous porphyry Cu mineralization. DMt grains showing partial hematite replacement yield ca. 55–20 Ma dates regardless of source, overlapping regional warm/wet climatic intervals. We interpret Cenozoic dates to reflect exhumation to near-surface oxidizing conditions and(or) supergene weathering. Magnetite is thus a promising target phase for (1) tracking the spatiotemporal distribution of porphyry systems, and (2) linking the formation and exhumation of these systems to a regional geologic history, both in Alaska and globally.

Alaska, Yukon↗

USGS2025

Evidence for offset of Cretaceous plutons by the Tintina fault in eastern Alaska: Implications for regional metallogeny

Cretaceous magmatism in eastern interior Alaska is voluminous, but temporally and spatially diverse – suggestive of varying sources and drivers. More than 150 new U-Pb zircon and more than 500 geochemical analyses of Cretaceous plutonic units allow for the grouping of distinct plutonic suites. Magmatism was continuous from 120-66 Ma but can be grouped into temporally distinct pulses from ca. 115-100 Ma, 100-90 Ma, and 75-66 Ma. Geochemical diversity occurs during each pulse, further distinguishing multiple suites. Diverse metallogenic epochs are strongly correlated to pluton chemistry. Mineralization is largely absent prior to 108 Ma. From 108-100 Ma, plutonism is coeval with sparse, but notable Au-quartz veins with variable Bi, As, W, and Mo. From 100-90 Ma, intrusion-related mineralization zones from Au-Cu(-Bi) and U-Th in the northwest to central Au- Bi-As-Te(-W), and Mo-W to the southeast. Porphyry style Cu-Mo(-Au) occurrences occur with the latest Cretaceous plutons emplaced from 75-66 Ma . Restoration of ~450 km of dextral movement on the Tintina fault and comparison of metallogenic and geochemical characteristics of Alaska plutons suggest 100-90 Ma plutons may be the continuation of the metallogenically significant Tombstone, Mayo, and Tungsten suites from the Yukon.

Alaska↗

USGS2025

Deformation mechanisms in quartz veins and shear zones elucidate the origin of gold mineralization at Pogo, Alaska

Pogo is a quartz vein hosted, ca. 8 Moz gold deposit. Although it has similarities to orogenic and magmatic-hydrothermal deposits, its origin remains enigmatic. Observations from surface exposures, underground workings, and drill core provide new constraints on quartz vein origins with implications for mineralization. Abundant, largely barren metamorphic segregation quartz veins are found throughout interior Alaska and share characteristics with mineralized quartz veins at Pogo. Pogo quartz veins show crystal plastic deformation fabrics consistent with greenschist to amphibolite facies metamorphism and a lack of internal shear. In contrast, gold in Pogo quartz veins occurs in brittle microfaults and fractures with sulphides such as arsenopyrite and pyrrhotite. Major and minor cataclastic shear zones also exist at Pogo. Cataclastic shear zones commonly cut the mineralized quartz veins and porphyroclasts are dominated by quartz with the same plastic deformation fabrics found in the major Pogo quartz veins. The porphyroclasts, and the carbonaceous clay-rich matrix they sit in, also contain gold indicating that the shear zones postdate quartz and earliest gold deposition. These observations suggest that competency contrasts between the quartz veins and their phyllosilicate-rich host rocks controlled transient permeability formed by late, preferential brittle deformation events localizing sulphide ± gold deposition.

Alaska↗