Sample descriptions and gold analyses of gold-bearing sedimentary rocks (northwest Wyoming) reported on in U.S. Geological Survey Circular 541

1975 ◽  
Author(s):  
J.C. Antweiler ◽  
W.L. Campbell
Author(s):  
Arthur Russell

Of the many small manganese deposits which have in the past been worked in both Cornwall and Devonshire that of Treburland is from the mineralogical point of view by far the most remarkable, its especial interest being due to the variety of minerals which it has afforded and to the fact that it and one other are the only manganese deposits in the west of England which are known to lie on the contact of igneous and sedimentary rocks and which have consequently been vitally affected by contact metamorphism.The following observations are based on frequent visits to the spot since the year 1906, when I first stumbled across the locality, which, strange to say, has only received very cursory mention by the Geological Survey and has altogether escaped mention in mineralogical literature.


Geophysics ◽  
1966 ◽  
Vol 31 (6) ◽  
pp. 1078-1087 ◽  
Author(s):  
G. V. Keller ◽  
L. A. Anderson ◽  
J. I. Pritchard

The electrical properties of rocks deep in the crust and in the upper part of the mantle may be studied with various electrical methods. The U. S. Geological Survey has conducted such studies using three methods: conventional galvanic resistivity surveys, inductive resistivity surveys using the magnetotelluric field, and the measurement of electrical properties of rock samples at high temperatures. By combined sample measurements, galvanic resistivity measurements and magnetotelluric studies, the resistivity profile through the crust and upper mantle may be defined more closely than has been possible previously. We have recognized the existence of a heterogeneous surface layer consisting of sedimentary rocks and weathered igneous and metamorphic rocks. Within the crust, a marked decrease in resistivity is sometimes observed at depths of about 10 kilometers, perhaps corresponding to the Conrad discontinuity sometimes recognized by seismologists. It has not been possible to recognize an electrical boundary at depths corresponding to those at which the Mohorovičić discontinuity is noted by seismologists. However, a marked decrease in electrical resistivity occurs at somewhat greater depths, between 60 and 100 km.


2017 ◽  
Vol 43 (2) ◽  
pp. 697 ◽  
Author(s):  
E. Manoutsoglou ◽  
A. Batsalas ◽  
E. Stamboliadis ◽  
O. Pantelaki ◽  
I. Vakalas ◽  
...  

During recent decades many studies have be done on the rocks that developed in the area of Western Greece and especially in Epirus, known in geoscientific literature as Ionian Zone of External Hellenides. These rocks have undergone geological research (basic geological mapping, research for hydrocarbons, metals and inert materials) and exploitation (inert materials). Recently, within the sedimentary succession of the Ionian zone submarine fans, in the region of Peta–Kompoti, in the prefecture of Arta, have been identified positions where sedimentary gold is present. Recently, positions where sedimentary gold is present, within the sedimentary rocks of the submarine fans, in the region of Peta–Kompoti, prefecture of Arta, have been identified. For the continuation and the practical application of these positive results, it was necessary to obtain a documented reference of geological parameters. After a series of new sampling and detailed analysis of the samples, this work presents the detected gold concentrations, illustrates the limits of grouping areas of interest as well as delineating and illustrating palaeogeographic factors that have contributed to the creation of gold-bearing formations. The highest gold concentration found was in the Ta Bouma sequence. The observation of constant indications of high gold values above background that suddenly increase in certain places up to 260 ppb, leads to the conclusion that in the broader area and within locations with equivalent formations procedure, there could be gold pockets of exploitable concentrations.


Author(s):  
Arthur Russell

Topaz, so common an accessory in tin lodes in all parts of the world, has hitherto been looked upon as comparatively rare in Cornwall. When massive, or even in the form of small, well-developed crystals, it is a mineral easily overlooked, or apt cursorily to be mistakcn for quartz.The presence of topaz as a microscopic accessory in granite, greisen, and rarely elvans, from most of the Cornish masses, has been determined by Dr. J. S. Flett in the course of the work of the Geological Survey; while the late Mr. J. H. Collins was responsible for the record of other interesting localities.In the present notes I have collected all the available information respecting its mode of occurrence and localities ; and have added several new ones, at some of which the mineral occurs in considerable mass, thus affording evidence that topaz is in Cornwall, as in the case of other countries, a comparatively common associate of cassiterite and wolframite, both in granite and sedimentary rocks.


During the past few years numerous deep boreholes have been sunk in the search for the gold-bearing reefs of the Witwatersrand system, beneath thick covers of younger formations, in the southern Transvaal and adjoining parts of the Orange Free State. The opportunity for temperature determinations in these boreholes is being utilized by the Geological Survey of South Africa, but a considerable time will elapse before the investigations are completed and the results become available. It therefore seems desirable that the publication of Dr E. C. Bullard’s conductivity determinations of representative rock samples from the two deepest boreholes in which the temperatures have been measured should be accompanied by an account of these investigations. The two boreholes, on the farms Gerhard- minnebron No. 4 near Potchefstroom and Jacoba No. 878 near Bothaville, were selected for the conductivity determinations on account of their depth and also because of the exceptionally small amount of change in the stratigraphic columns. For the sake of comparison three other boreholes are included in the description. In this paper the term “geothermic step” is used to indicate the increase in vertical depth corresponding to a rise in temperature of 1° C.


1872 ◽  
Vol 9 (94) ◽  
pp. 161-164 ◽  
Author(s):  
G. W. ◽  
F. M. Balfour

The interesting relation between the Porphyrite of Whitberry Point, at the mouth of the Tyne near Dunbar, and the adjacent sedimentary rocks, was first noticed, we believe, by Professor Geikie, who speaks of it in the Memoirs of the Geological Survey of East Lothian, pages 40 and 41, and again in the new edition of Jukes's Geology, pp. 269. The volcanic mass which forms the point, consists of a dark felspathic base with numerous crystals of augite: it is circular in form, and is exposed for two-thirds of its circumference in a vertical precipice facing the sea, about twenty feet in height.


Sign in / Sign up

Export Citation Format

Share Document