Interpreting Mars Surface Fluid History Using Minor and Trace Elements in Jarosite: An Example from Post Pit, Nevada

Size: px

Start display at page:

Download "Interpreting Mars Surface Fluid History Using Minor and Trace Elements in Jarosite: An Example from Post Pit, Nevada"

Dwain Murphy
5 years ago
Views:

1 Interpreting Mars Surface Fluid History Using Minor and Trace Elements in Jarosite: An Example from Post Pit, Nevada Paul Burger Collaborators: Jim Papike, Chip Shearer, Jim Karner

2 Courtesy BACKGROUND

rover at Meridiani Planum locality on Mars, in a

3 BACKGROUND Jarosite and hematite were first identified by the Mossbauer spectrometer aboard the Opportunity rover at Meridiani Planum locality on Mars, in a jarosite/hematite bearing outcrop known as El Capitan. Courtesy JPL

BACKGROUND: WHY STUDY JAROSITE? Unfortunately, instruments aboard MER could not give us detailed chemical information, but future missions (MSL) may be able to do so.

4 BACKGROUND: WHY STUDY JAROSITE? Unfortunately, instruments aboard MER could not give us detailed chemical information, but future missions (MSL) may be able to do so. Jarosite may be an important indicator of fluid rock interaction; applicability to terrestrial environments has been discussed by Papike et al. Can jarosite tell us about its formation history/environment; should we have a future sample return mission, is this a mineral we should try to recover? Crater Diameter = 800m

BACKGROUND - JAROSITE Formula = AB 3 (XO 4 ) 2 (OH) 6 A = 12 fold coordination Contains monovalent cations K, Na, Rb, etc. Divalent cations Ca, Pb, Ba, Sr, etc. Trivalent cations REE etc.

5 BACKGROUND - JAROSITE Formula = AB 3 (XO 4 ) 2 (OH) 6 A = 12 fold coordination Contains monovalent cations K, Na, Rb, etc. Divalent cations Ca, Pb, Ba, Sr, etc. Trivalent cations REE etc. NH 4 + or H 3 O + Or B = Octahedral coordination Trivalent cations Fe, Al, V Divalent cations Pb, Zn, Mg Tetravalent cations V X = Tetrahedral site Contains S, Sb, V 5+, As 5+, P 5+ etc.

6 ANALYTICAL CONDITIONS A suite of 14 jarosite samples was initially categorized; later analyses focused on fewer samples. Samples were analyzed using a combination of electron microprobe (EPMA) imaging and point analyses, and secondary ion mass spectrometery (SIMS). Analytical conditions were optimized for the elements analyzed; jarosite is susceptible to electron beam volatilization due to its high concentration of K, Na and S. Courtesy

7 SAMPLE SUITE Apex Mine, AZ (Supergene) Goldfield, NV (Hypogene) Quartz Jarosite Goldfield, NV (Hypogene) Alunite Apex Mine, AZ (Supergene) Jarosite

8 RESULTS MAJOR ELEMENT CHEMISTRY Al / (Al + Fe) AFU Apex Mine, AZ Gold Hill, UT Post Pit, NV Pena Blanca Others Goldfield Na / (Na + K) AFU

9 RESULTS MAJOR ELEMENT CHEMISTRY EDS mapping of Apex Mine, AZ revealed that zoning is intimately related to the relative abundances of Na and K. With respect to Apex Mine, there is an overall trend toward more sodic composition during later crystallization; superimposed on this is a micron-submicron scale zoning between jarosite and natrojarosite. 200 µm 3 2 1

10 Post Pit, NV

11 Post Pit, NV 50 µm

12 Post Pit, NV

13 Post Pit, NV TRAVERSE 1 A.F.U S - MAJ K - MAJ P - MIN Ba - MIN Distance (Microns)

14 Post Pit, NV TRAVERSE P - MIN Ba - MIN V X 3 - MIN Sr X 3 - MIN A.F.U Distance (Microns)

15 Post Pit, NV BUBBLE DIAGRAM P Coupled Substitution: Ba 2+ + P 5+ = K + + S 6+ Springcreekite: BaV 3 (PO 4 ) 2 (OH,H 2 O) 6 Ba P, V, As, Ba, Sr (afu) V As Sr 0.0

16 REE AVERAGE ANALYSES SAMPLE / CI CHONDRITE Apex Mine Gold Hill Post Pit Pena Blanca 0.01 Ce Nd Sm Eu Gd Dy Er Yb

17 CONCLUSIONS I. Trace Element Crystal Chemistry of Jarosite Growth zones occur in most samples, and can be characterized by changes in major element chemistry (e.g. Na and K), or by enrichment in minor/trace elements (Ba, Sr, V, P, etc.). The predominant coupled substitution mechanism found in the Post Pit, NV sample is: K + + S 6+ = (Ba 2+ or Sr 2+ ) + (P 5+ or As 5+ ) Vanadium is likely to be predominantly 3+ in this sample, as opposed V 4+ or V 5+ which one might expect in the oxidizing environment of jarosite deposition. Cerium valence in jarosite appears to be a potential indicator of fluid redox conditions; a lack of a Ce depletion in the Post Pit, NV sample seems to suggest a more reduced fluid than the other jarosite samples analyzed and is consistent with reduced V 3+ found in this sample.

18 CONCLUSIONS II. Relevance to Mars Surface Processes It is apparent from this study that trace elements and REE in terrestrial jarosite are valuable recorders of surface processes and may indicate the extent and possibly the duration of fluid interaction. The utility of jarosite as a recorder of fluid history demonstrates its potential value in understanding history of the martian surface. Our ability to decipher surface history using mineralogical indicators is dependent on having samples in hand, and underscores the need for a martian sample return mission.

Breeding et al., Data Repository Material Figure DR1. Athens. Study Area

Breeding et al., Data Repository Material Figure DR1. Athens. Study Area Breeding, Ague, and Brocker 1 Figure DR1 21 o 24 Greece o A 38 o Athens Tinos 37 o Syros Attic-Cycladic Blueschist Belt Syros Kampos B Study Area Ermoupoli N Vari Unit Cycladic HP-LT Unit Marble horizons