Workshops

NEOGENE BORATE DEPOSITS: Mineralogy, Petrology, Sedimentology
A workshop with special emphasis on the Anatolian deposits
October 4, 2012
by Cahit Helvacı (1), Federico Orti (2), Javier Garcia-Veigas (3), Laura Rosell (2), İbrahim Gündoğan (1)
(1) Dokuz Eylül Üniversitesi, Mühendislik Fakültesi, Jeoloji Mühendisliği Bölümü, 35100 Bornova, İzmir, Turkey;
(2) Departament de Geoquímica, Petrologia i Prospecció Geològica, Facultat de Geologia, Universitat de Barcelona, Zona Universitària de Pedralbes, 08028 Barcelona, Spain;
(3) CCiT, Universitat de Barcelona, Zona Universitària de Pedralbes, 08028 Barcelona, Spain

 

 Borates constitute a group of mineral deposits of great economic interest. Although several genetic types have been identified (volcanic, hydrothermal, metamorphic, sedimentary), the most important corresponds to those deposits formed in nonmarine, evaporitic settings. Lacustrine basins related to volcanic domains in which borates have precipitated are known in the stratigraphic record since the Oligocene, although those of Miocene age are the most relevant. The borate minerals in all these basins were generated in saline lakes placed in volcanogenic (mainly pyroclastic) terrains with intense hydrothermal influence, under arid to semiarid conditions, and in some cases at low temperatures. As other evaporitic deposits, the origin and composition (chemical and mineralogical) of the borate deposits can be appropriately documented by means of petrologic and sedimentologic approaches (lithofacies analysis, cyclicity, facies belts and depositional sequences).

The purpose of this workshop is to introduce the participants to the petrology and sedimentology of the Neogene borate deposits in Anatolia (Turkey) and, to a lesser extent, in the Andean region (La Puna, Argentina), although references to those deposits in western USA and in the Tibet Plateau (China) will be done.

The workshop is divided in four sections: The first section is an Introduction to the borate deposits and deals with some general mineralogical, chemical and sedimentological aspects. The second section summarizes the Lithofacies and Petrography of the most common borates: ulexite, probertite, inyoite, meyerhofferite, colemanite, priceite, howlite, borax, kernite, hydroboracite, kurnakovite and tunellite, among others. Some of them are rock-forming minerals. The third section presents examples of the depositional Cycles and Successions present in the Holocene and Neogene deposits (borates, borates-sulfates, and borates-sulfates-chlorides). The fourth section discusses aspects of some Examples of Neogene Borate Basins in Anatolia (Bigadiç, Kestelek, Kırka, Sultançayır, and Emet basins) and in La Puna region (NW Argentina). In the case of the Emet and the Kırka basins, the discussion is mainly based on accurate mineralogic/petrologic observations of borehole core samples under an Environmental Scanning Electron Microscope.

Workshop materials consist of: field and quarry profiles and images, lithologic borehole logs, hand samples, thin sections, and SEM images.

Workshop Program
Morning program
Introduction
Boratiferous lakes during the Miocene; mineralogic associations, major and accessory minerals; facies; subenvironments and depositional cycles
Ca-borates
Deposits: Emet and Kestelek districts (Turkey)
Major minerals: colemanite, meyerhofferite, inyoite
Na/Ca-borates
Deposit: Bigadiç district (Turkey)
Major minerals: ulexite, colemanite
Na-borates
Deposit: Kırka district (Turkey)
Major minerals: borax, tincalconite, kernite; ulexite, colemanite
Deposit: Kramer (Boron) district (USA)
Major minerals: borax, tincalconite, kernite; ulexite, colemanite
Afternoon program
Borates in association with sulphates
Deposit: Sultançayır district (Turkey)
Major Minerals: priceite/pandermite, howlite; gypsum, anhydrite
Deposit: Monte Amarillo district (Puna, NW Argentina)
Major minerals: hydroboracite, colemanite; gypsum, anhydrite
Borates in association with sulphates and chlorides
Deposit: Emet district (subsurface information; borehole samples)
Major minerals: probertite, colemanite, hydroboracite; glauberite, anhydrite, halite


HEAVY MINERAL ANALYSIS FROM ANATASE TO ZIRCON
"Methods, provenance analysis, diagenesis, hydrothermal alteration, weathering, placer-type deposits, ore guides"
October 5, 2012
by Harald G. Dill
Federal Institute for Geosciences and Natural Resources,
P.O. Box 51 01 53, D-30631 Hannover, Germany
E-mail: dill@bgr.de
Homepage: www.hgeodill.de

 

Heavy minerals (HM), pertaining to a group of minerals which exceeds the specific gravity of most rock-forming light minerals such as quartz and feldspar (2.35 to 2.84 gr/cm 3), are common to many clastic rocks such as sand and sandstones, including pyroclastic deposits equivalent in grain size. They are less widespread in argillaceous and calcareous sediments where the energy regime is rather low and thus conditions are less favorable for the development of allogenic HM accumulations. Authigenic HM are not lithology – controlled and may form in a wider range of sedimentary deposits wherever the physico-chemical conditions allow for their development.

Different methods are used for HM analysis. Routine HM analysis relies on HM separates in the grain size fraction from 0.020 mm to 0.600 mm, using heavy liquids of 2.95 g ml -1, e.g. tetrabromethane or non-toxic Na-polywolframate for separation and the petrographic microscope for their identification. At an advanced level microscopy is supplemented by SEM- EDX and EMPA. The CAMSIZER technique has proved to be a successful tool to study morphometric and granulometric issues and discriminate the way of transport and accumulation of placer minerals. Single grain dating by means of LA-ICP-MS techniques or fission track dating provide more accurate age data of HM and give an insight into the erosion history, uplift of source rocks and basin subsidence. Micro-Raman spectrometry of mineralogical characteristics of HM concentrates from placer deposits improves efficiency of separation of zircon.

Provenance analysis is one of the major fields of application of HM analysis. It contributes to the basin analysis of platform and foreland sediments as well as to the reconstruction of the source area by telling us the “unroofing story” of the basement.

Another strong point of HM analysis lies in the fields of, paleoenvironmental analysis and diagenetic studies, where these minerals can help to assess the creation of secondary porosity during deep burial which is essential for hydrocarbon exploration and assist in constraining the P-T regime of host rocks. Hydrothermal alteration may leave its imprint on sedimentary rocks and accumulate opaque and transparent minerals at a proximal or distal position relative to a venting system of hydrothermal fluids. Heavy minerals may be used in this case as a “proximity indicator”. In stream sediments of alluvial and fluvial depositional environments opaque and transparent HM may be used in a similar way as an “ore guide” to localize primary ore/ mineral deposits in the catchment area of a drainage system. Generally, HM are present only as accessory minerals in the sedimentary rocks, sometimes at a quantity of 0.x %. In placer deposits, however, the quantity is increased and ilmenite, rutile, “leucoxene”, zircon, monazite, xenotime, garnet, chromite and magnetite become valuable heavy minerals (VHM) as they achieve economic grades in different types of placer deposits. Their sedimentary deposits may be subdivided into eluvial, residual, colluvial, alluvial-fluvial (favorable environments and traps zones are point and braided bars, potholes, riffles, gravel lag), littoral-coastal (favorable traps zones are nearshore bars, shoals, drowned river mouth deposits) and aeolian (coastal and inland dunes) placer deposits. Based upon their diagenetic overprinting and the age of deposition, economic geologists used to distinguish “modern placers” from “paleoplacers”, examplified among others by the Precambrian U-Au placer deposits.


The study may be extended also to man-made chemical compounds, which fall outside of what might be called the mineral kingdom, such as mining and smelting residues and other artifacts. A detailed microscopic study of modern stream sediments reveals a lot of artificial products among the HM sensu stricto, which may shed some light on the history of manufacturing and archeometallurgy in a specific region. Even this approach based on artifacts may successfully be used for economic geology (“If you look for a mine look near a smelter”). Old bronzes or slags in the drainage system might guide the way of an exploration geologist through the smelting site to the ore deposit where the kiln feed came from. Smelters often are sites where ore from different deposits of a region were delivered to.

The HM analysis is held to be a method of interest to academicians and geologists working in the various fields of applied research and teaching. The one-day course is designed for (economic) geologists, sedimentologists, geographers, historians and archeometallurgists.


__________________________________________________________________________________________________

 

footer footer footer footer footer footer footer footer footer footer footer footer footer

__________________________________________________________________________________________________

 

Top banner image is after Taymaz et.al. (2007) The Geological Society of London, ISBN: 978-1-86239-239-7)