Geochemical Alteration Research Articles

Identification of diagnostic geochemical alteration in the wallrocks of archean volcanic-exhalative massive sulfide deposits

The present investigation is concerned with the identification of diagnostic lithogeochemical alteration signatures around volcanic-exhalative massive sulfide deposits in the Superior Province, with the overall objective of deriving lithogeochemical criteria, applicable in the search for new deposits of this type. Previous work on these deposits has indicated that, in general, the footwall alteration halo is marked by iron and magnesium enrichment, and calcium and sodium depletion. These features are often only detectable if the over-riding effects of igneous differentiation are compensated. It is apparent that the relative contribution of individual elements to the geochemical alteration varies from deposit to deposit, preventing the recognition of any universal geochemical alteration criterion. The role of discriminant analysis has been examined to establish the possibility of the technique indicating a more reliable expression of geochemical alteration. Discriminant analysis establishes the optimum weighted combination of variables to distinguish two or more populations from each other, in this case mineralized from barren environments. The application of the procedure to the data relating to the composition of wall rock associated with eight volcanic-exhalative massive sulfide deposits has drawn attention to the existence of two distinct types of alteration. The Joutel and Poirier deposits are characterized by Fe 2 O 3 , MgO, Zn and Ag enrichment, and CaO and Na 2 O depletion; this alteration style has been termed the “Joutel” type. At the South Bay, Sturgeon Lake and Mobrun deposits, Na 2 O is also strongly depleted, but Fe 2 O 3 and MgO are usually depleted and K 2 O is strongly enriched; this alteration style has been termed the “South Bay” type. Both of these alteration styles are displayed at the Mattabi and East Waite deposits. “Joutel” type alteration appears to be in close spatial association with discharge vents, while “South Bay” alteration is more laterally widespread and is representative of at least one deposit thought to be formed distally from its associated discharge vent. These geochemical signatures are more strongly expressed in pyroclastic rocks, and andesites, relative to massive rocks, and rhyolites. The geochemical alteration patterns delineated in this way constitute significantly larger exploration targets than the readily observable mineralogical alteration haloes. Results of the current investigations indicate that the mineralizing processes associated with Archean volcanic-exhalative massive sulfide deposits have given rise to more than oversimplification to aim exploration at the detection of a single type of response. The application of discriminant analysis provides a potential means of identifying and comparing as many responses as are present at the deposits studied. In this respect it is superior to any univariate statistical method, and has considerable application in exploration.

ESTUDO TERMODINÂMICO TEÓRICO APLICADO Á GÊNESE E ÁS ALTERAÇÕES DE HIDROXIFOSFATOS NATURAIS: FOSFATOS LATERÍTICOS DE JANDIÁ (PA) e PIROCAUA (MA).

This paper reports a theoretical thermodynamic study in order to relate the geochemical alterations involving lateritic profiles, enriched in aluminium- and aluminium-calcium hidroxy-pbosphates - Pirocaua (MA) and Jandia (PA) - as well as, iron phosphate and ironcalcium hydroxy-phosphate - Jandia (PA). Theoretical calculations and the use of thermodynamic data (standard free energies and solubility products) reveal some important conclusions about chemical equilibria, mineral formation, solubility and stability relations.

Effect of geochemical alteration of petroleum on composition of the light hydrocarbons

The objective of the research presented is to determine which geochemical criteria are significant in the alteration of the light hydrocarbon fraction of petroleum. Capillary gas-liquid chromatography was used to study the gasoline fractions of 100 samples taken form Mesozoic and Cenozoic petroleum deposits in Ciscaucasia. Signs of thermocatalytic and supergene transformations of the gasoline fractions are found which are characteristic of these processes. The significance of the criteria is tested statistically. (JMT)

New Applications of Electrical Methods in Hydrocarbon Exploration: ABSTRACT

Although electrical techniques have been used in the search for hydrocarbons since the pioneering work of the Schlumberger organization in the early 1920s, advances in seismic exploration quickly surpassed the structural mapping capabilities of surface electrical methods. Since that time, a variety of electrical techniques have remained in use, but impressive claims, even including direct detection of hydrocarbons, have remained largely unsubstantiated. Certain basic electrical methods continued to be used successfully in minerals exploration during the past 3 decades, however, and recent advances (both theoretical and technological) in these well-substantiated methods have generated new interest in electrical methods as a useful tool in oil exploration. Extensive research since 1977, including more than 350 line-mi (525 line-km) across 36 fields and prospects in a variety of both structural and stratigraphic traps has yielded several interesting results, some of which are inconsistent with past research. It does appear, however, that geochemical alterations above hydrocarbon accumulations are frequently detectable by conventional electrical techniques, and recent advances in these techniques are proving to be even more successful. In a parallel to seismic techniques, proper processing of the data appears to be the key to successfully detecting alterations associated with oil and gas reservoirs. End_of_Article - Last_Page 243------------

Geochemical dispersion in wallrocks associated with the Norbec deposit, Noranda, Quebec

Increasing emphasis is being given to the search for blind mineral deposits and the presence of geochemical dispersion halos in wallrocks may significantly enhance the chances of exploration success. Accordingly, the nature of wallrock dispersion associated with the Lake Dufault Cu-Zn-Au-Ag massive sulphide deposit, Noranda, Quebec, was examined to see if any such patterns existed. On the basis of relatively well defined geology, the area offered an opportunity to establish the relation between geochemical alteration and metallogeny, texture, structure and mineralogy. Anomalous element contents spatially related to mineralization are confined to the stratigraphic footwall (Waite Rhyolite) where Na 2O, SiO 2 and possibly CaO depletions and total Fe 1 Mn and MgO enrichments can be related to the hydrothermal vent. Dispersion halos 150–500 m in diameter are at least twice as wide as the obvious mineralogical alteration halo. Cu, Zn, Ag and S distributions show roughly similar patterns which are not obviously related to the main alteration pipe but do reveal broad enrichment zones in the general area of mineralization. The dispersion appears to be partly controlled by texture. Because of greater primary permeability, the halos produced in rhyolite breccia are wider and better defined than those in more massive rhyolites. On a wider scale (10 km 2) dispersion patterns are related to the fault and fracture systems of the area. As many as five stages of metamorphism have affected the area, altering all rocks to some extent. Samples can be classified petrographically into alteration groups, both related and unrelated to mineralization. Comparison of these groups reveals the inadequacy of certain elements for outlining alteration related to mineralization. For example, the range of K 2O in relatively unaltered rhyolite overlaps the composition of all other groups, including those related to mineralization. Similarly apparent is that the distribution of certain elements, e.g., Na 2O, may adequately define one part of an alteration zone such as the sericite-rich zone, but not another. It is concluded that careful use of lithogeochemistry in conjunction with detailed geological mapping and core logging can provide information otherwise obtainable only by time-consuming petrographic analysis. Thus it can be a potent weapon in the search for blind ore deposits.

The health impact of geochemical alterations associated with coal resource development in midwestern U.S.A.

It is projected that over the next 5 years surface coal mining in the United States will increase drastically. Because coal is a dirty fuel, mining and other geochemical changes in the environment may lead to increased health hazards. An epidemiologic study of possible risk factors associated with these geochemical alterations is presented. Mortality data and water quality data are analyzed and presented in the form of computer generated maps. A predictive model for use by the Environmental Protection Agency pertaining to the identification and control of pollutants is discussed.

Mineralogy and Provenance of Pleistocene Lake Clay in an Alpine Region

Ice-dammed lakes of Wurm age occupied pre-existing valleys in the Subalpine ranges of southeastern France. One of these, Lac du Trieves, accumulated over 200 m of predominantly clayey sediments in the form of varved and laminated deposits. The clay mineralogy of these sediments consists of the following suite: mica (65 to 85 percent), iron-rich chlorite (10 to 30 percent), and small amounts of poorly crystallized mixed-layer material. Bedrock lithologies in the vicinity of the lake vary from Jurassic and Cretaceous shale, silty shale, and carbonate rocks to Carboniferous meta-sedimentary rocks and Hercynian basement rocks. Jurassic shale, especially of the “terres noires” facies, consists primarily of an allevardite-type, regularly interstratified mica-montmorillonite and in some places directly underlies lacustrine sediments. The lack of incorporation of this material in lake clay indicates a relatively low surface erosion rate during Wurm maximum glaciation and suggests that mechanical and possibly geochemical alteration of metamorphic mica derived from the cirque areas accounts for the bulk of the lake clay formed.

Geochemical Alterations in Ground Waters of the Los Angeles Coastal Plain

Journal AWWAVolume 39, Issue 5 p. 423-429 Article Geochemical Alterations in Ground Waters of the Los Angeles Coastal Plain Carl Wilson, Carl WilsonSearch for more papers by this author Carl Wilson, Carl WilsonSearch for more papers by this author First published: 01 May 1947 https://doi.org/10.1002/j.1551-8833.1947.tb20551.xCitations: 2AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume39, Issue5May 1947Pages 423-429 RelatedInformation

The surgical Technic of total pneumectomy: Archives of Surgery, 1936, 32, 218.

Pirie, I.D. and Nichol, I., 1981. Geochemical dispersion in wallrocks associated with the Norbec deposit, Noranda, Quebec. In: A.W. Rose and H. Gundlach (Editors), Geochemical Exploration 1980. J. Geochem. Explor., 15: 159–180.Increasing emphasis is being given to the search for blind mineral deposits and the presence of geochemical dispersion halos in wallrocks may significantly enhance the chances of exploration success. Accordingly, the nature of wallrock dispersion associated with the Lake Dufault Cu-Zn-Au-Ag massive sulphide deposit, Noranda, Quebec, was examined to see if any such patterns existed. On the basis of relatively well defined geology, the area offered an opportunity to establish the relation between geochemical alteration and metallogeny, texture, structure and mineralogy.Anomalous element contents spatially related to mineralization are confined to the stratigraphic footwall (Waite Rhyolite) where Na2O, SiO2 and possibly CaO depletions and total Fe, Mn and MgO enrichments can be related to the hydrothermal vent. Dispersion halos 150–500 m in diameter are at least twice as wide as the obvious mineralogical alteration halo. Cu, Zn, Ag and S distributions show roughly similar patterns which are not obviously related to the main alteration pipe but do reveal broad enrichment zones in the general area of mineralization.The dispersion appears to be partly controlled by texture. Because of greater primary permeability, the halos produced in rhyolite breccia are wider and better defined than those in more massive rhyolites. On a wider scale (10 km2) dispersion patterns are related to the fault and fracture systems of the area.As many as five stages of metamorphism have affected the area, altering all rocks to some extent. Samples can be classified petrographically into alteration groups, both related and unrelated to mineralization. Comparison of these groups reveals the inadequacy of certain elements for outlining alteration related to mineralization. For example, the range of K2O in relatively unaltered rhyolite overlaps the composition of all other groups, including those related to mineralization. Similarly apparent is that the distribution of certain elements, e.g., Na2O, may adequately define one part of an alteration zone such as the sericite-rich zone, but not another.It is concluded that careful use of lithogeochemistry in conjunction with detailed geological mapping and core logging can provide information otherwise obtainable only by time-consuming petrographic analysis. Thus it can be a potent weapon in the search for blind ore deposits.