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

Courtesy http://www.windows.ucar.edu

BACKGROUND

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

•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:

WHY STUDY JAROSITE?

Formula = AB3 (XO4 )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.

Or

NH4+ or H3 O+

B = Octahedral coordination

Trivalent cations Fe, Al, V

Divalent cations Pb, Zn, Mg

Tetravalent cations V

X = Tetrahedral site

Contains S, Sb, V5+, As5+, P5+ etc.

BACKGROUND - JAROSITE

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 http://www.uam.es/docencia/microbio

SAMPLE SUITE

Apex Mine, AZ (Supergene)

Goldfield, NV (Hypogene)

Apex Mine, AZ (Supergene)Goldfield, NV (Hypogene)

Alunite

Jarosite

JarositeQuartz

RESULTS – MAJOR ELEMENT CHEMISTRY

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

0.0 0.2 0.4 0.6 0.8 1.0Na / (Na + K) AFU

Al /

(Al +

Fe)

AFU

Apex Mine, AZGold Hill, UTPost Pit, NVPena BlancaGoldfieldOthers

1

23

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

Post Pit, NV

50 µm

Post Pit, NV

Post Pit, NV

0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

2.25

0 25 50 75 100 125 150 175 200

Distance (Microns)

A.F

.U.

S - MAJK - MAJP - MINBa - MIN

Post Pit, NV – TRAVERSE 1

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0 25 50 75 100 125 150 175 200

Distance (Microns)

A.F

.U.

P - MINBa - MINV X 3 - MINSr X 3 - MIN

Post Pit, NV – TRAVERSE 1

0.0

0.1

0.2

0.3

0.4

0.5P,

V, A

s, B

a, S

r (af

u)

P

SrV

As

Ba

Post Pit, NV – BUBBLE DIAGRAM

Coupled Substitution: Ba2+ + P5+ = K+ + S6+

Springcreekite: BaV3 (PO4 )2 (OH,H2 O)6

REE – AVERAGE ANALYSES

0.01

0.10

1.00

10.00SA

MP

LE /

CI C

HO

ND

RIT

E

Apex MineGold HillPost PitPena Blanca

Ce Nd Sm Eu Gd Dy Er Yb0.01

0.10

1.00

10.00SA

MP

LE /

CI C

HO

ND

RIT

E

Apex MineGold HillPost PitPena Blanca

Ce Nd Sm Eu Gd Dy Er Yb

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+ + S6+ = (Ba2+ or Sr2+) + (P5+ or As5+)

• Vanadium is likely to be predominantly 3+ in this sample, as opposed V4+ or V5+ 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 V3+ found in this sample.

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.