Hornfels


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hornfels

[′hȯr‚felz]
(petrology)
A common name for a class of metamorphic rocks produced by contact metamorphism and characterized by equidimensional grains without preferred orientation.

Hornfels

 

a dense, fine-grained rock produced by the action of an instrusive body on the enclosing rocks. Hornfels differs in composition from the rocks that have been metamorphosed. Clay rocks become hornfels containing cordierite, andalusite, sillimanite, garnet, biotite, and feldspars. Basalts, basalt tuffs, and graywackes become hornfels with pyroxenes, basic plagioclase, and hornblende. Marls become hornfels with wollastonite, olivine, spinel, and carbonates. As the quantity of carbonates increases, hornfels become contact marbles.

References in periodicals archive ?
Large zones of auriferous biotite hornfels and silicification within late Paleozoic to Triassic sediments appear to be related to weakly deformed and intensely propylitic altered diorite plugs and stocks in the Copper Mountain area.
8) Total 509 (100) 577 (100) Table 2: The number of core types per raw material for both assemblages Assemblage Core type Basalt Chert Hornfels Quartz Booroola 3 Bifacial 6 Bipolar 1 Unifacial 1 11 Mount Bifacial 1 1 Alexina 1 Bipolar 2 Microblade Multifacial 2 Unifacial 1 1 1 Assemblage Core type Silcrete Total Booroola 3 Bifacial 1 7 Bipolar 1 Unifacial 5 17 Mount Bifacial 1 3 Alexina 1 Bipolar 2 Microblade 2 2 Multifacial 1 3 Unifacial 3 6 Table 3: The number and (percentage) of artefact types per raw material for both assemblages Assemblage Artefact type Quartz Silcrete Booroola 3 Broken flake 278 (66.
The aureole is larger in the north and east margins (up to 75 m) where metasedimentary calcareous rocks were metamorphosed to diopside-plagioclase-calcite-garnet-quartz hornfels (Lookwood, 1965).
In the study area lithological units is outcrops the second to fourth periods, which from old to new are as follows: phyllite, ouartzite, paragneiss, marble, shell, sandstone with tufa, volcanic rocks, crystalline limestone locally with fosolina, metamorphic volcanic and tufa, cherty limestone, phyllite, metamorphic quartzarenite, micaschist, metadolomite, amphibolite, limestone, shale and sandstone, schist hornfels, orthogneiss, granodiorite, oput rock, shale and phyllite sandstone, granite, granodiorite, diorite, dolomitic lime, radiolarit breccia, rodist lime, orbitoline, radiolarat, black and blue marl with limestone, alluvium.
Importantly, the gold intercept was hosted entirely in oxidized hornfels breccia, representing the most significant oxidized gold mineralization found to date in the northern Railroad project area.
Three types of copper-polymetallic mineralization are observed within the Project, these include skarn, hornfels and porphyry hosted mineralization.
Drill hole GHD007 is oriented toward the NE, and was designed to target the NE edge of Hobbs Pipe 1 near the surface, and then continue on to test the geology beneath historical highly anomalous hornfels metasediment hosted mineralisation.
Very low artefact densities indicate that Phase D, the most recent occupation trace, represents a different use of the site associated with substantially reduced use of opaline, enhanced presence of hornfels, a complete absence of backed microliths, and access to both pottery and iron (two small corroded objects, one directly dated to the eighth/ninth centuries cal AD; 1290[+ or -]30 BP; GrA-26831).
An exception to the use of poor quality raw material are the Dingcun lithic assemblages, which were produced predominantly on local dark hornfels, a high quality raw material for stone tool making (FIGURE 4).
Many areas of magnetic highs from the survey correlate with known pyrite hornfels zones and some areas of magnetic lows could represent buried intrusive plugs.
Targets range from the large scale Buccaneer Porphyry to several high grade zones including Old Pirate, Old Pirate South and the TB Hornfels Targets.