Record Details
Geology of the Quartzburg Mining District, Grant County, Oregon
ScholarsArchive at Oregon State University
| Field | Value |
|---|---|
| Title | Geology of the Quartzburg Mining District, Grant County, Oregon |
| Names |
Johnson, Floyd Raymond
(creator) Field, Cyrus W. (advisor) |
| Date Issued | 1975-06-12 (iso8601) |
| Note | Graduation date:1976 |
| Abstract | The Quartzburg District is seven miles north of Prairie City in east-central Grant County, Oregon. The District is in a pre-Tertiary window of volcanic, plutonic, and sedimentary rocks ranging from Permo-Triassic to Eocene-Oligocene in age. The Permo-Triassic Dixie Butte volcanics consist of thick basalts and andesites with minor volcanic breccias and intercalated argillite, chert, and conglomerate. This unit was moderately to intensely fractured by closely spaced faults prior to the emplacement of plutons of Early or Middle Triassic age. These plutons include spinel peridotite, gabbro, and granodiorite. Serpentinite is found in and adjacent to the ultramafic plutons. A second episode of intrusion is represented by the Late Jurassic Dixie Creek granodiorite. The Dixie Creek granodiorite is a concentrically zoned pluton, which changes in composition gradationally from a thin (less than 30 meters in width) marginal diorite, through granodiorite, to a core of quartz monzonite. The granodiorite portions of the pluton fed north-striking dacite porphyry dikes. Magmatic segregations of chalcopyrite and pyrite are present in the diorite phase. A potassiumargon age determination on biotite from this pluton yielded a 145 m. y. date (Thayer and Brown, 1964). Sedimentary rocks of mid-Cretaceous age are present in the northern and southwestern parts of the District. They include chert pebble conglomerate, sandstone (lithic arenite), and a single exposure of mudstone. Dikes of basaltic and andesitic breccia, rhyolite, and basalt of the Eocene-Oligocene Clarno Formation intruded the older pre-Tertiary terrain and fed flows that covered large portions of the Quartzburg District. Deposits of air-fall tuff breccia and minor siltstone and calcareous mudstone are intercalated with the flow rocks. During mid-Miocene time, the rocks of the District were covered by flows of the Strawberry volcanics and the Columbia River Group. Uplift of the Blue Mountains Anticline and subsequent erosion has exposed the pre-Tertiary rocks. Erosion of the mineral-bearing veins has produced rich placer deposits in Dixie Creek and the John Day River. Explosive eruption of Mt. Mazama during Recent time left deposits of volcanic ash along hill slopes and in topographic depressions. Structural evidence suggests a post Eocene-Oligocene age for mineralization. The Clarno Formation is crosscut by west-northwest to northeast-trending faults. These are in turn crosscut by northeast to east-trending faults which, along with the permeable contact zones of the dacite porphyry dikes, guided the mineralizing fluids from a source at depth. These fluids formed rich mesothermal gold-quartz veins and hypothermal copper-tourmaline massive sulfide veins and replacement deposits. |
| Genre | Thesis/Dissertation |
| Topic | Geology -- Oregon -- Quartzburg District |
| Identifier | http://hdl.handle.net/1957/44159 |
