IOCG Style Alteration of the Amargosa Prospect Baja California Norte, Mexico MacIntyre, T., Eckberg, E., Morgan, C., Enns, S., Cruise, M., & Hitzman, M. GSA 2005 Salt Lake City, Utah
Outline Location Methods Background Alteration Paragenesis Conclusions
Location Map - Baja
Methods Mapping and Sampling (by Steve Enns) Petrography Thin section (transmitted and reflected light) SEM (qualitative mineral chemistry) Analysis of Geochemical Data Whole rock Trace element Utilize data and thin section investigation to develop paragenetic sequence
Background Regional Geology Extensive bi-modal volcanism Interbedded volcaniclastics and sedimentary rocks Mid-late Cretaceous plutons Local Geology Intermediate volcanic rocks of the Alisitos Group Major diorite intrusion north of prospect
Alisitos Group Volcaniclastic
Alteration Paragenesis Sodic Sodic Calcic-Sodic 1 Potassic Si-B 1 Calcic-Sodic 2 Si-B 2 albite biotite epidote actinolite chlorite eu. magnetite an. magnetite eu. hematite an. hematite mushketovite radiating tour. blocky tour. quartz pyrite chalcopyrite
Albite Hematite laths Alteration Stage 1 Sodic Alteration Groundmass altered to albite alb hmt z Sample 12876: Hematite and albite +Na, +Al, +Fe; (-Si, -Ca, -K)
Alteration Sodic Calcic-Sodic 1 Calcic-Sodic 1 Potassic Si-B 1 Calcic-Sodic 2 Si-B 2 albite biotite epidote actinolite chlorite eu. magnetite an. magnetite eu. hematite an. hematite mushketovite radiating tour. blocky tour. quartz pyrite chalcopyrite
2 nd Alteration Stage Calcic-Sodic 1
2 nd Alteration Stage Calcic-Sodic Albite, epidote, euhedral magnetite, and mushketovite (hem mgt) +Ca, +Na, +Fe, +Al; (-Si, -K) Chl Mgt Sample 12889: Magnetite, chlorite Sample 12878: Epidote alteration
2 nd Alteration Stage (continued) Calcic-Sodic Py Mgt Sample 12844: Hematite laths replaced by magnetite (mushketovite); later pyrite replacing magnetite Hm
Alteration Sodic Calcic-Sodic 1 Potassic Potassic Si-B 1 Calcic-Sodic 2 Si-B 2 albite biotite epidote actinolite chlorite eu. magnetite an. magnetite eu. hematite an. hematite mushketovite radiating tour. blocky tour. quartz pyrite chalcopyrite
Biotite +K (minor) 3 rd Alteration Stage Potassic Chl Bio
Alteration Sodic Calcic-Sodic 1 Potassic Silica-Boron 1 Si-B 1 Calcic-Sodic 2 Si-B 2 albite biotite epidote actinolite chlorite eu. magnetite an. magnetite eu. hematite an. hematite mushketovite radiating tour. blocky tour. quartz pyrite chalcopyrite
4 th Alteration Stage Silica-Boron 1 Radiating Tourmaline
4 th Alteration Stage Silica-Boron 1 (Silicification) Radiating tour, quartz, pyrite, (cpy) Py Sample 12891: Radiating tourmaline, quartz, and pyrite R. Tour Py Shown in reflected light above and with crossed polars to right R. Tour Qtz
4 th Alteration Stage (continued) +Si, +B, +S, (+Cu?) Silica-Boron 1 Mgt from 2 nd stage Pyrite Py Sample 12884: Euhedral magnetite from stage 2 replaced by pyrite
Alteration Sodic Calcic-Sodic 1 Potassic Si-B 1 Calcic-Sodic 2 Calcic-Sodic 2 Si-B 2 albite biotite epidote actinolite chlorite eu. magnetite an. magnetite eu. hematite an. hematite mushketovite radiating tour. blocky tour. quartz pyrite chalcopyrite
5 th Alteration Stage Calcic-Sodic 2 Albite, epidote, actinolite, chlorite, anhedral magnetite, anhedral hematite, mushketovite, martite, chalcopyrite? Epi R. Tour +Ca, +Na, +Fe; -K, -Si Sample 12883: Radiating tourmaline from previous stage with epidote replacement
Calcic-Sodic 2 Epi (continued) Act Mar Chl Hem Actinolite, epidote and martite Mushketovite, epidote, chlorite Mush Sample 12877: Chlorite, hematite Chl Epi
Alteration Sodic Calcic-Sodic 1 Potassic Si-B 1 Calcic-Sodic 2 Si-B 2 Silica-Boron 2 albite biotite epidote actinolite chlorite eu. magnetite an. magnetite eu. hematite an. hematite mushketovite radiating tour. blocky tour. quartz pyrite chalcopyrite
Providencia Area Tourmaline Vein Silica-Boron 2
6 th Alteration Stage Silica-Boron 2 (Silicification) Blocky (dark) tourmaline, quartz Pyrite and chalcopyrite in adjacent prospect +Si, +B, (+Fe, +S, +Cu) Sample 12866: Highly pleochroic brown and green dark tourmaline and quartz Tour
Alteration Sodic Calcic-Sodic 1 Potassic Si-B 1 Calcic-Sodic 2 Si-B 2 albite biotite epidote actinolite chlorite eu. magnetite an. magnetite eu. hematite an. hematite mushketovite radiating tour. blocky tour. quartz pyrite chalcopyrite Copper
Copper At Amargosa
Copper cpy Mar Martite (mgt to hem) with disseminated chalcopyrite Possible association of copper with magnetite.(?)
Conclusion Multiple alteration events have occurred Events are roughly divided into: Sodic (+Na, +Fe) Calcic-Sodic (+Ca, +Na, +Fe, -K) Minor Potassic (+K) Silicification (+Si, +B, +Fe, +S, +Cu?) these events recur at multiple stages, with slightly different assemblages This prospect appears to be an IOCG system with very little copper present in the samples analyzed.
Thank You Cardero Resource Corp. Steve Enns Mark Cruise Colorado School of Mines Murray Hitzman Geological Society of America Travel Grant