@article{PAR00002015,
  title = {6{H}ydrothermal alteration and magnetic properties of rocks in the {C}arolina de {M}ichilla stratabound copper district, northern {C}hile},
  author = {{T}ownley, {B}. and {R}operch, {P}ierrick and {O}liveros, {V}. and {T}assara, {A}. and {A}rriagada, {C}.},
  editor = {},
  language = {{ENG}},
  abstract = {{I}n the {C}arolina de {M}ichilla district, northern {C}hile, stratabound copper mineralization is hosted by {J}urassic volcanic rocks along the trace of the {A}tacama fault system. {I}n this study, we present the overall effects of hydrothermal alteration on the magnetic properties of rocks in this district. {T}wo types of metasomatic alteration associations occur, one of regional extent and the other of local hydrothermal alteration associated with copper mineralization (e.g., {L}ince-{E}stefania-{S}usana). {R}egional alteration is interpreted as a low-grade "propylitic association" characterized by an epidote-chlorite-smectite-titanite-albite-quartz-calcite association. {T}he local hydrothermal alteration is characterized broadly by a quartz-albite-epidote-chlorite-calcite mineral assemblage. {T}he most pervasive alteration mineral is albite, followed by epidote and, locally, actinolite. {T}hese minerals contrast sharply against host rock minerals such as chlorite, calcite, zeolite, prehnite, and pumpellyite, but alteration is constrained to mineralized bodies as narrow and low contrast alteration halos that go outwards from actinolite-albite to epidote-albite, to epidote-chlorite, and finally to chlorite. {H}ydrothermal alteration minerals, compared to regional alteration minerals, show iron-rich epidotes, a lower chlorite content of the chlorite-smectite series, and a nearly total albite replacement of plagioclase in the mineralized zones. {O}paque minerals associated with regional alteration are magnetite and maghemite, and those associated to hydrothermal alteration are magnetite, hematite, and copper sulphides. {W}e present paleomagnetic results from nine sites in the {M}ichilla district and from drill cores from two mines. {L}ocal effects of hydrothermal alteration on the original magnetic mineralogy indicate similar characteristics and mineralogy, except for an increase of hematite that is spatially associated with the {C}u-sulphide breccias with low magnetic susceptibilities. {R}esults indicate that it is impossible to magnetically differentiate mineralized bodies from unmineralized lavas, except for pyrite-rich hydrothermal breccias. {I}n conclusion, for stratabound copper deposits of the {M}ichilla type, the overall effect of hydrothermal alteration on the paleomagnetic properties of rocks is of low contrast, not clearly discernable even at a small scale. {F}rom an exploration point of view, magnetic exploration surveys should not discern mineralized bodies of {C}u-sulphide breccias except in detailed ground surveys due to the small size of contrasting bodies. {U}noriented drill cores with primary ore mineralization record a characteristic remanent magnetization of reverse polarity. {T}aking into account the azimuth and dip of the drill cores, we were able to compare the magnetization of the mineralized bodies with the characteristic directions from sites drilled in situ from {L}ate {J}urassic-{E}arly {C}retaceous intrusives mostly. {T}he characteristic direction recorded by the {P}luton {V}iera is similar to the magnetization of the ore bodies of the {E}stefania mine. {I}f copper mineralization mostly postdates the tilt of the volcanic flows, the low paleomagnetic inclinations suggest an age for the mineralization near 145 {M}a, the time of the lowest paleolatitude for the {S}outh {A}merican plate during the {M}esozoic.},
  keywords = {hydrothermal alteration ; rock magnetic properties ; stratabound {C}u mineralization ; {C}hile},
  booktitle = {},
  journal = {{M}ineralium {D}eposita},
  volume = {42},
  numero = {7},
  pages = {771--789},
  ISSN = {0026-4598},
  year = {2007},
  DOI = {10.1007/s00126-007-0134-6},
  URL = {https://www.documentation.ird.fr/hor/{PAR}00002015},
}