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Restricted Kriging as a combination of OK and IK
Published in Heping Xie, Yuehan Wang, Yaodong Jiang, Computer Applications in the Mineral Industries, 2020
The case study reported here involves a large data set collected from a disseminated epithermal gold deposit. Both RK and OK are applied to the same data set for comparison through cross validation and block modeling. RK is implemented by using two restriction conditions: a high-grade threshold and a low-grade threshold. The mineralization is hosted primarily by Precambrian metavolcanics and granitic rocks. Disseminated mineralization is best developed in the more mafic metavolcanic rocks as well as in mafic segregations within the granitic rocks. Strict geological boundaries between ore and waste in this deposit can not be easily drawn. Therefore, indicator kriging was conducted at cutoff 0.015 opt Au. The probability estimates were contoured and plotted out in East-West cross sections. Three major disconnected individual orebodies are clearly identifiable. Statistical analyses show no significant variations between the three orebodies.
Mining applications
Published in Duncan C. Wyllie, Christopher W. Mah, Rock Slope Engineering, 2017
Duncan C. Wyllie, Christopher W. Mah, Alan F. Stewart, P. Mark Hawley, Nick D. Rose, Brent W. Gilmore
Weak rock mass conditions can occur in many types of ore deposits, especially where ore deposition is associated with alteration or complex structural zones. The lithologies associated with these conditions can be considered to represent a wide range of geological environments including: (i) highly fractured plutonic rocks (e.g. copper porphyry deposits); (ii) metasedimentary or metavolcanic rocks (e.g. shear hosted gold deposits); or (iii) mafic volcanic rocks (e.g. asbestos deposits). This example is a generalized case history of combined experience at four operating mines with open pit slopes ranging from 300 to 500 m high. The main similarity between these projects is the presence of a weak rock mass associated with a near-vertical regional fault or shear zone, exposed in the lower portion of one of the pit walls, that defines a boundary to the ore body.
Lexicon of lithostratigraphic units for the Sudan
Published in J.R. Vail, Lexicon of Geological Terms for the Sudan, 2022
It consists of thick layers of metavolcanic rocks, weakly metamorphosed, dominantly intermediate in composition but with subordinate acid and basic lavas. Minor tuffs, agglomerate, spilites, etc. are present, as are intercalations of metasediments, pyroclastics, marbles, and schists. The Group is said to be represented by the lower part of the Nafirdeib Series. The rocks grade upwards, or in part laterally into the Upper Metasedimentary Group.
Assessing the Lithium Potential of the Paleoproterozoic Rocks of the West African Craton; the Case so Far
Published in Geosystem Engineering, 2023
The polycyclic crustal growth of the West African Craton was as a consequence of two major series of orogenic episodes, namely the Liberian events (2.7 Ga) and the Eburnean events (2.5–1.8 Ga) (Bessoles, 1977 as cited in Abouchami et al., 1990). The 2.5 Ga to 1.8 Ga event was first referred to as the Eburnean by Bonhomme (1962) who coined that name to describe a major orogenic event which affected the Birimian. There is however evidence supporting an earlier tectonomagmatic event known as the Leonian (3.0 Ga). The Leonian is predicted to have caused the accretionary growth of the Congo, Tanzania Cratons and the Man and Reguibat Shields (Boher et al., 1992). In the Leo-Man Shield, the Birimian terranes outcrop in the northeastern and southeastern portion within the West African Craton (Abouchami et al., 1990) and is composed mainly of metavolcanic and metasedimentary rocks intruded by granitoids of varying ages in Ghana (De Kock et al., 2012). The metavolcanic rocks include meta-basalts, meta-gabbros and meta-andesites, while the metasedimentary rocks include pelitic rocks like phyllites as well as greywackes and some quartzites (Eisenlohr & Hirdes, 1992).
Compositional characteristics of mineralised and unmineralised gneisses and schist around the Abansuoso area, southwestern Ghana
Published in Applied Earth Science, 2023
Raymond Webrah Kazapoe, Olugbenga Okunlola, Emmanuel Arhin, Olusegun Olisa, Daniel Kwayisi, Elikplim Abla Dzikunoo, Ebenezer Ebo Yahans Amuah
The Sefwi-Bibiani Greenstone Gold Belt is situated northwest of the Ashanti Greenstone Gold Belt and is underlain by metavolcanic and metasedimentary rocks that are granitoids and mafic units (Galipp et al. 2003; Senyah et al. 2016). The majority of the metavolcanic rocks are massive and pillow basalts, basaltic andesite, dacites, and rhyolites with tholeiitic to calc-alkaline signatures (Perrouty et al. 2012; Senyah et al. 2016). The majority of the metasedimentary rocks consist of phyllites, wackes, and a volcaniclastic unit with pyroclastics and epiclastics (Jessell et al. 2012; Perrouty et al. 2012). The metavolcanics and metasedimentary rocks are intruded by syn-volcanic tonalitic to granodioritic granitoids (Jessell et al. 2012). These granitoids have now been metamorphosed into various gneisses (Kazapoe et al. 2022). The Sunyani Basin is bordered to the west by the Sefwi-Bibiani Greenstone Gold Belt and to the east by the Kumasi Basin (Griffis and Agezo 2000).
Hydrothermal alteration, lithogeochemical marker units and vectors towards mineralisation at the Svärdsjö Zn-Pb-Cu deposit, Bergslagen, Sweden
Published in GFF, 2022
Anton Fahlvik, Tobias C. Kampmann, Nils F. Jansson
The Svärdsjö deposit has previously been classified as a Falun-type deposit (Levi et al. 1980), one of two types into which deposits in the BLU have historically been subdivided (Magnusson 1948; Sundblad 1994). The Falun-type largely corresponds to the stratabound volcanic-associated limestone-skarn-hosted (SVALS) type as defined by Allen et al. (1996). The SVALS-type deposits are characteristically Zn-Pb-Cu-Ag-Au deposits in dolomite marble and magnesian skarn after former limestone interbeds. Notable examples include the Garpenberg, Falun, Sala and Stollberg deposits. These deposits are commonly developed as systems of stratabound lenses, ranging in style from massive to vein networks and sulphide-cemented breccias with clasts of altered wall rock. Adjacent felsic metavolcanic rocks are commonly hydrothermally altered and metamorphosed to associations rich in quartz and mica (muscovite, chlorite, biotite). Metamorphic porphyroblasts are common, depending on bulk composition and metamorphic grade constituting garnet, amphibole, cordierite and/or aluminosilicates. The porphyroblasts commonly visually accentuate the chemical zonation patterns in the hydrothermally altered zones. Alteration is commonly most intense and widespread in the stratigraphic footwall, which locally hosts stringer-type mineralisation.