Lunar and Planetary Science XLVIII (2017)
2532.pdf
DIVERSE HYDROTHERMAL CONDITIONS AT LITTLE HOT SPRINGS VALLEY, LASSEN:
COMPARISON TO HOME PLATE, MARS. L. J. McHenry1, D. T. Dixon1,2, G. L. Carson1, and Christopher L.
Vickery1 1UWM Geosciences, 3209 N. Maryland Ave, Milwaukee, WI 53201 ([email protected],
[email protected]), 2Geology Department, Western Washington University, 516 High St, Bellingham, WA 98225
([email protected])
Introduction: Lassen Volcanic National Park has
the largest hydrothermal system in the Cascades, including a variety of hydrothermal environments [1]. Little
Hot Springs Valley (LHSV) in particular hosts a wide
range of hydrothermal conditions and associated deposits, including acid-sulfate fumaroles, mud pots, and hot
springs, near-neutral, travertine-depositing hot springs,
and near-neutral gypsum-depositing hot springs (Fig. 1)
[2]. These varied sources originate as part of the same
hydrothermal system in some cases within meters of
each other, revealing a complex system.
for temperature (T) and pH, and cooled water samples
to below 50°C for field analysis using a Hydrolab sonde
for T, pH, oxidation/reduction potential (ORP), Specific
Conductivity (SpCond), Total Dissolved Solids (TDS),
and salinity (sal). Lab analyses included X-ray Diffraction (XRD) for mineralogy and X-ray Fluorescence
(XRF) for geochemistry (methods of [7]).
XRD and XRF results: Sulfate minerals were
abundant and varied in LHSV altered sediments and
precipitates, reflecting varied conditions. Redox differences are shown in the presence of sulfates vs. sulfides
(Figures 2 and 3). XRD results reported in Table 1.
L"LV"14"21
LV%14%09
A
B
L"LV"14"22
L"LV"14"23
L%LV%14%3
LV%14%29
C
D
Figure 1: Field photos at LHSV. A: acid-sulfate fumarole,
with white sulfate precipitates (alunogen, halotrichite). B. Organic filaments and mineral precipitates in a near-neutral hot
spring. C. Hot spring related travertine deposit. D. acid-sulfate
mud pot (kaolinite dominated).
Figure 2: Samples collected near fumarole, showing smallscale mineralogy variations. The deepest sample (L-LV-1423) is mostly smectite and pyrite, while the shallower samples
have more quartz and sulfate minerals (alunite and alunogen).
XRD results from these three samples are shown in Figure 3.
1000"
Q
900"
Methods: We visited LHSV in 2014 and collected
water, rock, altered sediment/mud, and mineral precipitate samples from different hydrothermal contexts (see
examples in Figures 1 and 2). We tested thermal waters
800"
S
700"
CPS$(with$offset)$
Purported hydrothermal features near Home Plate,
explored by the Mars Exploration Rover Spirit at Gusev
Crater, have also been suggested to represent a range of
hydrothermal enviornments in a small area,Figure'3
including
acid-sulfate fluids or fumaroles [3,4] and near-neutral
sinter-depositing hot springs [5,6]. Comparison to similar deposits on Earth can help interpret these features,
and assess whether such diverse deposits require multiple, distinct alteration events or whether they could be
formed by one laterally varying hydrothermal system.
L"LV"14"21
Q
S
Al
Q
Q
600"
Q
500"
A
A
400"
300"
Q L"LV"14"22
Q A Q A Q
S
200"
S
100"
P SP
L"LV"14"23
P
P
P
0"
0"
10"
20"
30"
40"
50"
60"
Degrees$2$Theta$
Figure 3: XRD patterns for L-LV-14-21, 22, and 23 (Figure
2). Q = quartz, S = smectite, Al = alunogen, A = alunite, and
P = pyrite. Pyrite is present in the deepest sample (L-LV-1423), and sulfates are present in the shallower samples (samples
21 and 22), where quartz is also more abundant.
Lunar and Planetary Science XLVIII (2017)
2532.pdf
L"LV"14"3
L"LV"14"4
L"LV"14"5
L"LV"14"7
L"LV"14"9
L"LV"14"10
L"LV"14"11
L"LV"14"14
L"LV"14"16
L"LV"14"17
L"LV"14"20
L"LV"14"21
L"LV"14"22
L"LV"14"23
L"LV"14"29
Table&1:&XRD,determined&phases
s
s
s
s
p
s
s
p
p
p
c
s
s
s
p
Amorphous
Quartz
X
XXX XXX XXX XXX XX XX XXX XX
X
+
X
Sulfur
+
XXX XXX X
Pyrite
XX
Hemetite
+
Anatase
+
Calcite
Kaolinite
+
XXX
dominate the headwaters, while both near-neutral (gypsum-associated) and acidic (other sulfate-associated)
hot springs occur within meters of each other in the
lower part of the valley. The acidic springs are also more
saline and have higher TDS than the neutral springs.
While all water samples analyzed were at least slightly
reducing (ORP <0), the travertine precipitating hot
springs were the most extreme.
XXX
XX
Smectite
+
X
+
X
X
Substrate
Alunite
X
Alunogen
X
+
X
X
+
X
XX +
XXX +
X
X
XX
+
XXX X
Kalinite
X
+
XX
XX X
Tschermigite
X
Tamarugite
XX
Voltaite
XX
Jarosite
+
Quenstedtite
Halotrichite/M
Pickeringite
+
+
XX +
GypsumM
XX XX
XXX XX XX
Table 1: XRD-identified phases. s = altered soil, p = precipitate, xxx = abundant, xx = common, x = present, + = rare.
The “substrate” of LHSV is complex, including
both fresh andesite to dacite and blocks altered by previous episodes of hydrothermal alteration [8]. The ubiquity of quartz in the altered samples reflects both a silica-rich substrate and residual enrichment of silica during alteration. Enrichment reached 93% SiO2 in one
sample (L-LV-14-5), and enriched TiO2 in the same
sample (3.13%, compared to 0.74% in unaltered andesitic substrate) suggests residual enrichment, a likely result of acid-sulfate alteration. Samples near the headwaters of LHSV included travertine-precipitating hot
springs (Hydrolab results in Table 2); precipitates consisted almost entirely of calcite. In downstream areas,
gypsum was precipitated near near-neutral hot springs,
while other sulfates were more common near acidic hot
springs and fumaroles.
Table 2: 2014 Hydrolab results for Little Hot Spring Valley T pH ORP SpCond Sal TDS °C mV uS/cm ppt g/l Clear hot spring 80.3 2.6 -­‐99 5924 3.27 3.8 Murky hot spring 82.0 2.7 -­‐160 6170 3.41 3.9 Clear hot spring 91.0 6.8 -­‐314 409 0.20 0.3 Acid hot spring 75.0 2.4 -­‐153 9054 5.10 5.8 Travertine spring 65.7 7.5 -­‐488 1314 0.69 0.8 The Hydrolab results confirm a wide range of hydrothermal conditions in LHSV. Travertine springs
Discussion: The assemblage of precipitated minerals can be attributed at least in part to the characteristics
of the associated hydrothermal fluids, with clear asociations between pH, salinity, and minerals observed. Gypsum and calcite precipitate from more neutral fluids,
while Al-, Fe-, Mg-, and Na-sulfates occur near acidic
hot springs and fumaroles. Darker, pyrite-bearing
“mud” at depth points toward a shallow oxidation front,
with more reducing conditions below and more oxidizing conditions above. Geochemical trends were less
clear, since it is difficult to separate the different generations of hydrothermal alteration using bulk composition alone, but do show some examples of Si- and Tirich residual deposits formed by acid-sulfate leaching.
Mars comparison: The presence of near-neutral
and acid-sulfate hydrothermal conditions in close proximity could be comparable to what is inferred for hydrothermally altered deposits near Home Plate, though the
absence of opaline silica sinter associated with the neutral fluids at LHSV makes this analog less suitable than
others at Lassen (e.g. Growler hot spring). The hydrothermal conditions that favor precipitation of specific
sulfate mineral assemblages at LHSV could, however,
be used to help decipher the conditions needed to form
Martian sulfate deposits.
Acknowledgments: This research was funded by
the Wisconsin Space Grant Consortium. Thanks to Dr.
W.-S. Han for the use of the Hydrolab sonde, and to the
NPS for permission to sample within Lassen Park.
References:
[1] Ingebritsen S.E. et al. (2016) Am Mineral, 101,
343-353. [2] Thompson J.M. (1985) JVGR, 25, 81-104.
[3] Squyres S.M. et al. (2008) Science, 320, 1063-1067.
[4] Schmidt M.E. et al. (2009) EPSL,281, 258-266. [5]
Ruff S.W. et al. (2011) JGR, 116, E00F23. [6] Ruff
S.W. & Farmer J.D. (2016) Nat Commun 7, 13554. [7]
McHenry L.J. (2009) Chem Geol, 265, 540-552. [8]
John D.A. (2009) GSA Abstracts with Programs, 41(7),
525.