Hydrothermal alteration mineralogy in Newberry 2 drill core, Newberry Volcano, Oregon

1984 ◽  
Author(s):  
K.E. Bargar ◽  
T.E. Keith
Keyword(s):  
Hydrothermal Alteration ◽  
Drill Core ◽  
Newberry Volcano

Hydrothermal Sr contamination of the Dippin sill, Isle of Arran, Western Scotland

1984 ◽  
Vol 48 (348) ◽  
pp. 311-322 ◽  
Author(s):  
A. P. Dickin ◽  
C. M. B. Henderson ◽  
F. G. F. Gibb
Keyword(s):  
Stable Isotope ◽  
Hydrothermal Alteration ◽  
Closed System ◽  
Hydrothermal Systems ◽  
Hydrothermal Fluids ◽  
Drill Core ◽  
Sr Isotope ◽  
Core Section ◽  
High Silica ◽  
Isotope Measurements

Abstract The Dippin sill, which is emplaced into the Triassic sediments of SE Arran, is an alkaline basic sheet which displays pronounced hydrothermal alteration. The 40-m-thick sill has suffered pervasive contamination with radiogenic Sr, introduced from the Triassic sediments by hydrothermal fluids. Stable isotope measurements suggest that fluids were of meteoric origin, but were restricted to a small closed-system circulation. Initial 87Sr/86Sr ratios in the sill were raised from an original value of 0.7032 to a maximum of 0.7091, contamination being especially pronounced near the contacts at Dippin Head itself (localities 12 and 14) and in a drill core section through the sill above Dippin. Hydrothermal Sr was incorporated into an early-formed high-CaO, high-Sr analcime, which replaced unstable high-silica nepheline in interstitial patches. However, this high-CaO analcime, along with plagioclase, was later replaced by a low-CaO, low-Sr analcime, allowing Sr leaching from the margins of the sill. Hydrothermal fluids are thought to have migrated up to 1 km laterally, up the dip of the sill, mainly via tension joints forming in the cooling intrusion. Pooling of hot fluids at the upper end of the sill probably raised water/rock ratios in this region and allowed greater Sr contamination during mineralogical alteration. The undersaturated mineralogy of the sill accounts for its pervasive hydrothermal Sr contamination, which contrasts markedly with the relatively undisturbed Sr isotope compositions of Hebridean granites involved in hydrothermal systems.

ASSESSING HYDROTHERMAL ALTERATION INTENSITY IN VOLCANIC-HOSTED MASSIVE SULFIDE SYSTEMS USING PORTABLE X-RAY FLUORESCENCE ANALYSIS OF DRILL CORE: AN EXAMPLE FROM MYRA FALLS, CANADA

2020 ◽  
Vol 115 (2) ◽  
pp. 443-453
Author(s):  
Brian A. McNulty ◽  
Nathan Fox ◽  
J. Bruce Gemmell
Keyword(s):  
Hydrothermal Alteration ◽  
Detection Limits ◽  
Fluorescence Analysis ◽  
Massive Sulfide ◽  
Hydrothermal Systems ◽  
Geochemical Data ◽  
Drill Core ◽  
Sulfide Mineralization ◽  
X Ray

Abstract Current portable X-ray fluorescence (pXRF) technology can rapidly and inexpensively yield concentrations of geologically significant elements, typically with instrument detection limits below several tens of parts per million. Based on conventional XRF whole-rock geochemical data, both the Ishikawa alteration index and the chlorite-carbonate-pyrite index increase with proximity to sulfide mineralization at Myra Falls. However, available pXRF technology is typically unable to detect all the elements required to calculate these alteration indices. As a result, there is a need to utilize the elements that are readily detectable using pXRF and apply these to hydrothermal alteration assessment. We propose that Rb/Sr ratios provide a robust proxy for the Ishikawa alteration index and demonstrate that conventional whole-rock XRF analytical results for Rb and Sr can be reproduced using pXRF analysis from drill core surfaces. At Myra Falls, the Rb/Sr ratios vary from <0.1 for least altered rocks, 0.1 to 0.5 for weakly altered rocks, 0.5 to 1.0 for moderately altered rocks, 1.0 to 2.0 for strongly altered rocks, and >2.0 for intensely altered rocks. Downhole profiles of alteration intensity generated from systematic pXRF analysis of drill core surfaces can be used to inform drilling and targeting decisions. The application of the Rb/Sr ratio as a proxy for alteration intensity extends beyond this case study and can be applied to other hydrothermal systems that produce phyllosilicate minerals as alteration products of feldspar.

Low-temperature metamorphism and secondary components in the Portage Lake Volcanics: a reassessment

1993 ◽  
Vol 30 (7) ◽  
pp. 1404-1414 ◽  
Author(s):  
Huiling Li ◽  
S. Beske-Diehl
Keyword(s):  
Magnetic Properties ◽  
Hydrothermal Alteration ◽  
Remanent Magnetization ◽  
Drill Core ◽  
Upper Peninsula ◽  
The Core ◽  
Time Period ◽  
Core Section ◽  
Order Of Magnitude ◽  
A Minor

We studied the effects of hydrothermal alteration on magnetic properties of the magnetite and hematite components in the 1.1 Ga Portage Lake Volcanics, Upper Peninsula, Michigan. Results show the importance of the intensity and direction of the hematite magnetization in the detection of secondary magnetite overprints in basalts. We collected samples from 20 flows in two stratigraphic sections, one from outcrops and the other from drill core. The remanence unblocked below 590 °C during thermal demagnetization is considered to be due to magnetite, and that unblocked between 610–690 °C is considered to be due to hematite. Hematite remanent intensities in the flow interiors are an order of magnitude less intense than those of magnetite, and correlate with magnetite intensities from the top of the volcanics to the lower prehnite–pumpellyite zone (5.5 km depth) in the outcrop section and to the epidote–pumpellyite zone (7.0 km depth) in the core section. These magnetic properties are very similar to those of Recent Icelandic basalt flows. Below these depths, magnetite intensities decrease until they are equal to hematite intensities. Hematite remanent intensities do not consistently increase with depth, suggesting that secondary hematite produced during hydrothermal alteration is a minor contributor to hematite intensities. The magnetite directions become distinct from the hematite directions in the prehnite–pumpellyite zone (6.2 km depth). This difference in directions indicates an unresolved secondary overprint formed during hydrothermal alteration. We conclude that the magnetite component carries a secondary overprint; a conclusion that contrasts with that of a previous study. Thermo-viscous remanent magnetization obtained over a time period of 1–10 Ma near 300 °C would be enough to account for much of the secondary component.

Secondary mineralization and hydrothermal alteration in the Reydarfjordur drill core, eastern Iceland

1982 ◽  
Vol 87 (B8) ◽  
pp. 6511-6524 ◽  
Author(s):  
James M. Mehegan ◽  
Paul T. Robinson ◽  
John R. Delaney
Keyword(s):  
Hydrothermal Alteration ◽  
Drill Core

Progressive hydrothermal alteration associated with gold mineralization of the Zone 1 intrusion of the Callahan property, Val-d'Or region, Quebec

1989 ◽  
Vol 26 (12) ◽  
pp. 2495-2506 ◽  
Author(s):  
Cecilia L. Jenkins ◽  
Pierre Trudel ◽  
Guy Perrault
Keyword(s):  
Hydrothermal Alteration ◽  
Gold Mineralization ◽  
Drill Core ◽  
Average Composition ◽  
Free Gold ◽  
Gold Enrichment ◽  
White Colour ◽  
Grey Colour ◽  
Ore Grade ◽  
Felsic Rocks

The Zone 1 intrusion of the Callahan property, Val-d'Or, Quebec, is a relatively small (0.045 km2), pretectonic to syntectonic trondhjemitic mass that has been altered to varying degrees by progressive hydrothermal alteration. The entire intrusion is gold enriched, and the degree of mineralization is proportional to the degree of alteration. Examination of drill core reveals that visible colour variations are related to mineralogic and chemical alteration. Three degrees of alteration are identified: least, medium, and most-altered. The least-altered facies has a green–grey colour, whereas the medium-altered facies has a pale grey colour and the most-altered facies has a cream–white colour. As the intensity of alteration increases, the amount of albite, carbonate, and pyrite increases and the amount of phengite decreases. These progressive, mineralogic changes are correlated chemically to increases in Na2O, CO2, and S and to a decrease in K2O. The median gold values for least-, medium-, and most-altered trondhjemite are 42, 148, and 158 ppb, respectively, and the average gold values (excluding highly anomalous values) are 85, 172, and 188 ppb, respectively, indicating that gold enrichment is already advanced at the medium intensity of alteration. Despite its weak enrichment, tungsten is the most anomalous trace element of the typically gold-associated elements in lode deposits and is, therefore, of special interest. Gold, found principally in the medium- and most-altered facies, is most commonly observed as free grains in the gangue. It may also be associated with pyrite and, to a much lesser extent, with tellurides. The majority of the free gold grains have an estimated diameter between 20 and 60 μm, and their average composition is 95 wt.% Au and 5 wt.% Ag. This study and comparisons of the Zone 1 trondhjemitic intrusion with other gold-enriched, felsic intrusions in the Abitibi greenstone belt suggest that elevated sodium (i.e., albitization) and anomalous gold values, relative to barren felsic rocks, should be used to target ore-grade zones within pretectonic to syntectonic felsic intrusions.

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