UNIVERSIT‰ DU QU‰BEC L'UNIVERSIT‰ DU QU‰BEC .UNIVERSIT‰ DU QU‰BEC THˆSE ... l'orpiment et

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  • UNIVERSIT DU QUBEC

    THSEPRSENTE

    L'UNIVERSIT DU QUBEC CHICOUTIMIET

    L'INSTITUT DE GOCHIMIEL'ACADMIE CHINOISE DES SCIENCES

    POUR L'OBTENTIONDU DOCTORAT EN RESSOURCES MINRALES

    PAR

    GUAN-QING LU

    LE LIEN GNTIQUE ENTRE LA MINRALISATION EN OR ET EN

    MERCURE ET L'VOLUTION PTROLIFRE

    - LE CAS DE DPT D'OR ET MERCURE DE DANZHAI

    MAI 1994

  • bibliothquePaul-Emile-Bouletj

    UIUQAC

    Mise en garde/Advice

    Afin de rendre accessible au plusgrand nombre le rsultat destravaux de recherche mens par sestudiants gradus et dans l'esprit desrgles qui rgissent le dpt et ladiffusion des mmoires et thsesproduits dans cette Institution,l'Universit du Qubec Chicoutimi (UQAC) est fire derendre accessible une versioncomplte et gratuite de cette uvre.

    Motivated by a desire to make theresults of its graduate students'research accessible to all, and inaccordance with the rulesgoverning the acceptation anddiffusion of dissertations andtheses in this Institution, theUniversit du Qubec Chicoutimi (UQAC) is proud tomake a complete version of thiswork available at no cost to thereader.

    L'auteur conserve nanmoins laproprit du droit d'auteur quiprotge ce mmoire ou cette thse.Ni le mmoire ou la thse ni desextraits substantiels de ceux-ci nepeuvent tre imprims ou autrementreproduits sans son autorisation.

    The author retains ownership of thecopyright of this dissertation orthesis. Neither the dissertation orthesis, nor substantial extracts fromit, may be printed or otherwisereproduced without the author'spermission.

  • A Genetic LinkBetween the Gold-Mercury Mineralization and Petroleum Evolution

    -A case of the Danzhai Gold-Mercury Deposit

    By

    Guan-Qing LU

    A thesis in partial fulfllment of the requirements for the degree of Doctor ofPhilosophy at l'Universit du Qubec Chicoutimi, Chicoutimi, Qubec,Canada, and the Institute of Geochemistry, the Chinese Academy ofSciences, Guiyang, Guizhou Province, P. R. China.

    May 1994

  • Abstract

    The Danzhai gold-mercury deposit is situated in the eastern region of Guizhou

    province, southwest of P. R. China.

    The Danzhai deposit is one of the gold-mercury-antimony-barite deposits in the

    Sandou-Danzhai ore belt, which is controlled by regional fault system Fi. The host rocks are

    Upper Cambrian and Lower Ordovician carbonates. Wall rock alteration is dominated by

    silicification and carbonatization. The major mineral assemblages consist of cinnabar,

    arsenopyrite, stibnite, pyrite and realgar, orpiment as well as barite. Chemical analyses

    show that gold is positively correlated with arsenic so that the gold may be mainly associated

    with arsenic minerals. The Au/Ag ratio is always greater than 1 in the gold ore.

    Hydrocarbons, particularly bitumen, are abundant in both the host rocks and the ore. The

    geological characteristics of the Danzhai gold-mercury deposit is quite similar to that of

    Carlin gold deposit in the western U.S.A except the Danzhai deposit is rich in organic matter

    and not associated with igneous rocks.

    A number of gold-mercury-antimony-barite deposits are distributed in or around the

    Majiang-Danzhai oil trap, and all of these deposits are present under the ancient interface

    between petroleum and oilfield brine (-500 m). Field observation shows that a variety of

    forms of hydrocarbon occur not only in the host carbonates but in the ore deposit as well.

    Patch-like bitumen, veinlet bitumen as well as stylolite-like bitumen host sulfide minerals

    such as arsenopyrite and cinnabar while metal sulfides such as cinnabar and gangue minerals

    also host bitumen. Besides bitumen, paraffin wax is also found in the deposit. An organic

    petrography study demonstrates that the bitumen in the minerals from the deposit is identical

    to the bitumen in the former Majiang-Danzhai oil trap. The bitumen is actually pyrobitumen,

    with a high reflectance, a mosaic texture, and an anisotropic nature but without fluorescence.

    The reflectance of bitumen from the deposit is high, varying from 2 to 3.8%, and the

    temperature calculated from this reflectance ranges from 150 to 210C, indicating that the

    petroleum in the Majiang-Danzhai oil trap reached the thermal natural gas stage.

  • [ i

    Fluid inclusion examination reveals important information about the ore-forming

    fluids. A variety of hydrocarbon inclusions are identified, including: (1) liquid methane

    inclusions; (2) bitumen inclusions; (3) paraffin wax inclusions; (4) heavy oil inclusions, and

    various combinations. Liquid methane inclusions are found in both metallic minerals such as

    cinnabar and realgar and gangue minerals such as quartz, calcite, dolomite and barite. The

    heavy oil inclusions are more abundant in carbonate minerals such as calcite and dolomite

    than in other minerals such as quartz and cinnabar. The spatial relationship between the

    liquid methane inclusions and cinnabar and realgar demonstrates that the hydrocarbon

    inclusions are a significant part of ore-forming fluid. The homogenization temperatures of

    aqueous inclusions range from 130-210 C and the salinities detected from 5.2 - 19.3 wt.

    %NaCl equivalent. Solid probe mass spectrometry confirms that hydrocarbons, particularly

    methane, are the most important constituent of the fluid inclusions. The methane in some

    inclusions is as high as 69.8 mole percent. Some heavy hydrocarbon molecules are also

    detected by the mass spectra. The spectra of a sample from the second stage of

    mineralization displays a complete separation indicating a dominant unmixing of the CH4

    and H2O phases. Another spectra of a sample from the third stage of mineralization

    displays an complete separation indicating a marked unmixing of H2O and CO2 phases.

    Argon isotope data of three quartz samples from the Danzhai gold-mercury deposit

    show that the initial (40Ar/36Ar )o value is much higher than 295.5, the (40Ar/36Ar )o

    value of modern atmosphere, which is common in most formation waters or oilfield brines.

    The isochron ages for the three quartz samples are 2783 Ma, 3047 Ma and 2250 Ma

    respectively, which are obviously much older than reasonable mineralization age, even

    much older than that of Cambrian and Qrdovician host sedimentary rocks. This high excess

    argon is interpreted to be the result of the formation water or oilfield brine leaching

    radiogenic 40Ar from the Lower Cambrian black shale, subsequently precipitated in the

    Danzhai gold-mercury deposit.

    Lead isotope data exhibit characteristics of common, rather than radiogenic lead. They

    are homogeneous, and belong to highly evolved |i value lead, which are widely distributed

    over South China. These characteristics are different from the lead isotope data of

    Mississippi Valley-type lead zinc deposits, but similar to that of most stratiform deposits

  • 11

    hosted in sedimentary rocks. Lead isotope data in the deposit plots on the evolution curve of

    the Upper Crust in the plumbotectonic model. The model age of ore lead is in the

    neighborhood 400 Ma, equivalent to the end of Silurian period. Therefore, lead isotopes in

    the deposit indicate derivation from the host sedimentary rocks.

    Evidence described above suggests that gold and mercury mineralization in the

    deposit was related to the petroleum evolution in the Majiang-Danzhai oil reservoir. The oil

    and associated brine leached the metals and sulfur from the Lower Cambrian black shale and

    other host rocks and subsequently precipitated them to form the Danzhai deposit.

  • IV

    Rsum Prolong

    Le dpt d'or et de mercure de Danzhai, qui fait l'objet de cette tude, est situ dans

    le district oriental de Guizhou ( Chine du sud-ouest), province clbre pour sa production

    de mercure. Quelques cent dpts de mercure, antimoine, arsenic, or et barytine sont

    prsents dans ce district et dans la rgion voisine, la province de Hunan. Danzhai tait trs

    connu comme un des plus grands dpts de mercure en Chine. Il tait explor et exploit

    comme dpt de mercure pendant plus d'une trentaine d'annes.

    Ds le dbut des annes 1980, en comparant les caractres gologiques du dpt d'or

    et de mercure de Danzhai avec ceux du dpt d'or de type-Carlin dans l'ouest des tats-

    Unis, une rvaluation de la mine de mercure a t effectue pour trouver de l'or. Les

    travaux gologiques dtaille ont dmontr que la minralisation d'or est actuellement

    associe la minralisation de mercure, il est aussi d'une importance industrielle

    indpendante.

    1. L'environnement tectonique

    La colonne stratigraphique de la rgion orientale de la province de Guizhou est

    presque complte partir du Protrozoque jusqu'au Trias Infrieur-Moyen, et comprend les

    carbonates et les flyschs du Palozoque Suprieur, les carbonates du Palozoque Infrieur

    intercals occasionnellement par des shales et des roches lastiques protrozoques

    lgrement mtamorphises.

    L'environnement tectonique de la rgion orientale de Guizhou est encore

    problmatique. Le concept bien accept est que la Chine mridionale, particulirement la

    rgion d'tude, est situe dans le bouclier de Yangtze. Mais cette interprtation est remise en

    question par Hsii et al. (1988, 1989) qui proposent un modle de chevauchement. Les

  • diffrentes interprtations de l'environnement tectonique du sud de la Chine rsultent des

    diverses interprtations du Groupe de Banxi. Hsu et al. (1988, 1989) assument que le

    Groupe de Banxi est segment par un ocan ( ocan de Banxi), limit par deu

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