When a bolide hits a world class Pb/Zn deposit

new insights into the Lawn Hill impact structure

Jess A. Salisbury, Andrew G. Tomkins, Bruce F. Schaefer

    Research output: Contribution to conferenceAbstract


    The Lawn Hill Impact Structure is situated approximately 240km NNW of Mt Isa in north eastern Queensland, and consists of a ring of low Cambrian limestone hills overlying very weakly metamorphosed Proterozoic shales and other sediments. The world class Century Pb/Zn deposit sits at the margin of the structure and is hosted within the Proterozoic basement. The deposit exhibits strong indications of impact related brecciation previously attributed to other causes, or left unexplained. These include a variety of breccia textures, some incorporating the much younger Cambrian limestone, and ranging from micro to mega scale, including a one million tonne "megaclast" of Century-like ore encapsulated with Cambrian limestone adjacent to the main deposit. Other interpreted impact effects include milled limestone "breccia dykes" injected deep into the deposit and impact related hydrothermal remobilisation of ore minerals with small galena deposits observed within the Cambrian limestone. These were possibly formed through a process similar to Mississippi Valley Type Pb/Zn deposits. Additional results from a fluid inclusion study indicate that temperatures and fluid composition were within tolerances for remobilisation of Pb and Zn during impact-related fluid flow; however, sealing of flow paths and short lived convection may limit the size of possible impact-generated ore deposits. New constraints are placed on the age of the impact structure through 40 Ar/39 Ar dating of impact melt from the central uplift.
    Original languageEnglish
    Number of pages1
    Publication statusPublished - 2012
    EventInternational Geological Congress (34th : 2012) - Brisbane, Australia
    Duration: 5 Aug 201210 Aug 2012


    ConferenceInternational Geological Congress (34th : 2012)

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