Gold in the Farallones Block of the Shale-Hosted, Clastic-Dominated Castellanos Zinc-Lead Deposit (Northwest Cuba)

The Zn-Pb ores of the Castellanos shale-hosted, clastic-dominated deposit in northwest Cuba average nearly 1 g/t Au, with local maximum concentrations up to 34 g/t Au. This deposit is stratiform with respect to the bedding in the host black shales and shows a bottom to top zoning of ore assemblages made up of a stockwork underlying the main orebody, a basal pyrite-rich zone and a disseminated to massive Zn-Pb ore zone capped by a discontinuous, thin barite-rich zone. Petrographic data and textural relations allow distinguishing five textural types of pyrite (framboidal Py I, colloform Py IIa, euhedral Py IIb, massive Py IIc and banded colloform Py III) successively formed during ore deposition. The main Zn-Pb ore formed after the crystallization of disseminated, sedimentary framboidal pyrite (Py I) in black shales by the superimposition of several crystallization events. The crystallization sequence of the main ore-forming stage evolved from the precipitation of colloform sphalerite and pyrite (Py IIa) with skeletal galena and interstitial dolomite-ankerite to similar ore assemblages but showing subhedral to euhedral crystal habits (Py IIb) and interstitial calcite-rich carbonates. This stage ended with the development of massive pyrite (Py IIc), mainly occurring at the base of the stratiform orebody. A late fracturing stage gave way to the development of a new generation of colloform banded pyrite (Py III) just preceding the crystallization of early barite. Au is mainly concentrated in pyrite showing variable contents in the different textural types of pyrite and a bottom to top enrichment trend. Minimum contents occur in massive pyrite (Py IIc) from the basal pyrite-rich zone (0.18 ppm Au average), increasing in pyrite IIa (from 0.29 to 2.86 ppm Au average) and in euhedral pyrite (Py IIb) (from 0.82 to 9.02 ppm Au average), reaching maxima in colloform banded pyrite (Py III) formed just before the crystallization of early barite at the top of the orebody. Au enrichment in pyrite correlates with that of Sb (0.08–4420 ppm), As (0.7–35,000 ppm), Ag (0.03–1560 ppm) and to a lesser extent Cu (3–25,000 ppm), Ni (0.02–1600 ppm) and Mn (0.6–5030 ppm). Au deposition should have taken place by oxidation and, probably cooling, of reduced (H2S-dominated) fluids buffered by organic matter-rich black shales of the host sedimentary sequence. The input of such reduced fluids in the ore-forming environment most probably occurred alternating with that of the main oxidized fluids which leached Zn and Pb from the large volume of sandstones and siltstones making up the enclosing sequence, thus being responsible for the precipitation of the majority Zn-Pb ore. Supply of Au-carrying reduced fluids might progressively increase over the course of ore formation, reaching a maximum at the beginning of the late fracturing stage. This evolution of Au supply is consistent with the early crystallization of barite since Ba can also only be transported at low temperature by highly reduced fluids. These results highlight the potential of medium-sized, shale-hosted, clastic-dominated deposits to contain economic (by product) Au amounts and show that ore-forming fluids can change from oxidized (SO42+ dominated) to reduced (H2S-dominated), and vice versa, throughout the evolutionary history of a single deposit.

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Calyx plate homologies and early evolutionary history of the Crinoidea

The Paleontological Society Papers ◽

10.1017/s1089332600000309 ◽

1997 ◽

Vol 3 ◽

pp. 289-304 ◽

Cited By ~ 2

Author(s):

William I. Ausich

Keyword(s):

Evolutionary History ◽

History Of ◽

Competing Ideas ◽

Bottom To Top

New, competing ideas on crinoid plate circlet homologies and the desire for a phylogenetically-based classification have led to a reexamination of the Crinoidea. The most primitive crinoids had four plate circlets, from bottom to top: lintels, infrabasals, basals, and radials. Dicyclic camerates, cladids, flexibles, and dicyclic articulates are composed of infrabasals, basals, and radials. Monocyclic camerates and monocyclic articulates are composed of basals and radials. These all follow traditional ideas on homologies. In contrast, disparids with “compound radials” are composed of lintels, infrabasals, and radials, rather than “basals,” “inferradials,” and “superradials;” and disparids without “compound radials” have lintels and infrabasals rather than “basals” and “radials.”Parsimony-based phylogenetic interpretation of Ordovician crinoids with rhombiferans as the outgroup shows that crinoids are divisible into six clades, two paraphyletic and four monophyletic, including four-circlet crinoids, cladids, disparids, camerates, flexibles, and articulates.

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Originations and Extinctions in Brachiopods

The Paleontological Society Papers ◽

10.1017/s1089332600000991 ◽

2001 ◽

Vol 7 ◽

pp. 249-258

Author(s):

Paul Copper

Keyword(s):

Evolutionary History ◽

Western Europe ◽

Cold Water ◽

Taxonomic Description ◽

Exponential Increase ◽

History Of ◽

The 1960S ◽

Molecular Relationships ◽

New Generation ◽

Gains And Losses

Broad patterns of originations and extinctions of genera, as well as families and higher groups, have always interested those who study the fossil record (e.g., Sepkoski, 1984). They record an important part of the major changeovers, and thus the dynamics, of marine ecosystems over time (Droser et al., 1996; Droser and Sheehan, 1997). This seems especially true for the Paleozoic, when brachiopods were the dominant shelly animals on the seafloor in tropical, temperate, and even cold water settings. Attempts have also been made to determine turnover patterns at the species level (Patzkowsky and Holland, 1997), though this is a much more difficult task, as the validity of species depends a great deal on the skills of the taxonomist. A similar problem is the comparative analysis of diversification data based on a single continent, e.g., North America, as related to others (Miller, 1997a, b); though Laurentia is probably better studied than most areas except western Europe. The exercise of studying broad-scale generic gains and losses for the brachiopods is at the present time preliminary (only three volumes of the revised Treatise are published). The 1965 Treatise contains fewer than 25% of the genera known in detail and described today, with an almost exponential increase in taxonomic description since the 1960s (Williams, 1996). Since then, there have been dramatic revisions and re-interpretations of the evolutionary history of the major brachiopod families, as a new generation of brachiopod workers arrived and matured. We also have a considerably improved knowledge of molecular relationships within the Brachiopoda (Cohen and Gawthrop, 1996). Sound taxonomy is the fundamental basis for sound theoretical discussion of the nature and origins of major changeovers in phyla such as the Brachiopoda. Unfortunately, there are presently relatively few, active brachiopod specialists, as taxonomy has given way to other, more general interests.

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Elaborating the role of reflection and individual differences in the study of folk-economic beliefs

Behavioral and Brain Sciences ◽

10.1017/s0140525x18000274 ◽

2018 ◽

Vol 41 ◽

Author(s):

Kevin Arceneaux

Keyword(s):

Decision Making ◽

Individual Differences ◽

Cognitive Processes ◽

Evolutionary History ◽

Behavioral Responses ◽

History Of ◽

Economic Beliefs

AbstractIntuitions guide decision-making, and looking to the evolutionary history of humans illuminates why some behavioral responses are more intuitive than others. Yet a place remains for cognitive processes to second-guess intuitive responses – that is, to be reflective – and individual differences abound in automatic, intuitive processing as well.

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