GEOCHEMISTRY OF HIGHLY ALKALINE WATERS OF THE COAST RANGE OPHIOLITE IN CALIFORNIA, USA

Altered waters impacted by serpentinization of Coast Range Ophiolite (CRO) ultramafic units have been reacting with trapped Cretaceous seawaters, meteoric waters, and other surface derived waters since tectonic emplacement of this ophiolite. In 2011, groundwater monitoring wells of various depths were established near Lower Lake, CA, USA in the McLaughlin Natural Reserve, administered by the University of California-Davis, in order to understand ongoing low temperature alterations and biogeochemical interactions taking place. Wells were installed at two sites in the Reserve. There are three Quarry Valley area wells (QV1-1 [23m depth], QV1-2 [14.9m], QV1-3 [34.6m]) and five Core Shed area wells (CSW1-1 [19.5m], CSW1-2 [19.2m], CSW1-3 [23.2m], CSW1-4 [8.8m], CSW1-5 [27.4m]). Water samples were collected from all installed wells, as well as from an older well drilled near the historic core shed (Old Core Shed Well, or OCSW [82m]), and an upper (TC1) and lower (TC2) site sampling a nearby groundwater-fed alkaline seep, at Temptation Creek. Key environmental parameters (temperature, pH, conductivity, oxidation-reduction potential, and dissolved oxygen) were collected in the field using YSI-556 multiprobe meter, and total concentrations for major cations (Ca, Na, Mg, K) were analyzed using Thermo Scientific iCAP 7400 Inductively Coupled Plasma-Atomic Emission Spectrometry, and anions (F, Cl, SO4 , NO3 ) on Dionex Modular DX 500 Ion Chromatography. Principal component analysis was conducted to determine key factors and processes controlling water chemistries at CRO. Geochemist’s Workbench software was used to model the low temperature alteration of a serpentinization-influenced model water volume passing through serpentinite over a period of 100 million years. Modeling provided insight into the changing pH, Eh, evolving water chemistries, stepwise mineral assemblages, appearance of marker minerals at geochemical transitions in the system, and supported evidence of pervasive impacts of low temperature, oxidative weathering of serpentinites. This work supports the case of incremental dilution and transformation of a deeply sourced Ca-OH Type II water in this environment, and constrains reaction status of present day CRO waters and those of similar sites, in terms of the progress of serpentinite weathering reactions. Further, the study informs our understanding of serpentinization-related geological environments present on other celestial bodies (e.g., Mars, Europa, Enceladus) in our Solar System and beyond.

( Cardace et al., 2013). Here, the Middle to Late Jurassic CRO exposures represent deformed and structurally dismembered segments of oceanic crust and uppermost mantle, now incorporated within the continental block (Dickinson et al., 1996), that are undergoing a unique process of long-term aqueous alteration, characterized as vigorous serpentinization ( Figure 1) followed by low temperature, oxidative weathering.
Serpentinization is the process during which ultramafic mantle rocks rich in olivine and pyroxene react with water, leading to formation of serpentinite rock that is dominated by serpentine group minerals including lizardite, chrysotile and antigorite (Moody, 1976). This water-rock reaction is accompanied by the generation of fluids with high concentrations of hydrogen (Corliss et al. 1981;Russell, 2007;Ehlmann et al, 2010), increase in rock volume, and release of heat energy (Allen and Seyfried, 2004 Simultaneously, this ability of microorganisms to survive also provides explanation and insight into synthesis of organic compounds needed in the origination of life on Earth (Lang et al., 2010, Martin et al., 2008. Another important area of significance and ongoing research involves serpentinization for its role in carbon sequestration (carbon capture and storage, CCS).
The hyperalkaline serpentinizing waters contain almost no dissolved inorganic carbon (DIC). When these waters reach the surface or get discharged, atmospheric carbon dioxide is rapidly taken up and converted into insoluble carbonates (Burns & Matter, 1995;Chizmeshya et al., 2007;Andreani et al., 2009;Kelemen et al., 2011;Paukert et al., 2012). This presents a way to store the increasing and alarming concentrations of carbon dioxide from the atmosphere and is now an active area of ongoing research with a promising potential of reversing the effects of anthropogenic global warming (McCollom et al., 2013).
Given these recent scientific research interest in serpentinites, the objective of this paper is to develop a more thorough understanding of the serpentinite weathering, geochemistry of the serpentinizing fluids, serpentinite rock-water interactions, and changes in mineralogy and fluids chemistry with the passage of time.
The interaction of the serpentines with water and causing the resulting waters to undergo unique chemical changes was first reported and studied by Barnes and colleagues in 1967. Barnes compared the ionic concentrations of the unusual ultrabasic spring samples from Red Mountain in California, John Day in Oregon, and Cazadero in California, and proposed that these unusual waters were genetically related to serpentinization (Barnes et al., 1967). Later, in 1977, Barnes (Barnes & O'Neil, 1977).
In 2012, Paukert et al., characterized the ionic makeup of spring and well water samples from Samail ophiolite using ion chromatography (IC) on a Dionex 2000 with an AS18 column for the anions, and inductively coupled plasma atomic emission spectrometry (ICP-AES) with Horiba Jobin-Yvon Activa M with PFA nebulizer for the cations (Paukert et al., 2012). The resulting geochemistry of waters were classified as being of two different types: those that were high in the Mg 2+ and -HCO3 -(named Type I waters), and those with high Ca +2 and -OH -(named Type II waters).
The serpentine soils are unique as they are naturally deprived in nutrients that plants need; instead they are rich in Mg, Fe, and trace elements that include Ni, Cr, Cd, Co, Cu, and Mn (Wildman et al., 1968, D'Amico & Previtali, 2012. This creates a challenging environment for plants to grow in. The serpentine endemic species are visibly different from other plants growing in a landscape with serpentine soil exposures and have evolved and shown adaptations that fit this unique environment (Safford et al., 2005;Alexander, 2007). Due to their harsh nature, the serpentine soils at Coast Range locale and other similar sites have been studied from an ecological point of view. How they weather under natural environments is little studied as yet.
Also, the weathering processes tend to differ site to site due to differences in topography, parent rock mineralogy, climate and rainfall.
It is proposed that CRO is a site of on-going low temperature serpentinization leading to production of different fluids that are reflective of rock-water interactions.
A reaction pathway can be modeled to explain the temporal changes in mineralogy and fluid chemistries. To confirm this, water samples were collected from Coast

Climate
The reserve receives an average precipitation of 75.7 cm per year, with the average temperatures of July as 24.6 ºC and January's average temperature of 7.3 ºC (Natural Reserve System University of California, 2018). Regional climate is Mediterranean-type, with summers being dry and hot, and winters wet and cold (Mathany & Belitz, 2015).

Hydrogeology
The movement of groundwater follows the area's topography and the direction of flow of the surface water features. The recharge to groundwater is primarily through the precipitation and runoff from surface water features (Mathany & Belitz, 2015).

Sampling Locations
Eight monitoring wells were installed near Lower Lake, CA, in the McLaughlin The two other sampling sites (TC1 and TC2) include an upstream and downstream point along a seasonally active ground-water fed creek, the Temptation Creek (TC). TC1 is the area where the groundwater seep is emerging from, and TC2 is the percolating water before it disperses into the landscape. The distance between TC1 and TC2 is about 515m with a relief of 65m ( Figure 3).
Samples were collected via syringes (rinsed three times) fitted with 0.22 µm pore size filters. No pretreatment was required for IC samples, which were stored in clean, plastic laboratory bottles and frozen until analysis. The samples for ICP-AES were collected in certified 100 ml Nalgene bottles, spiked with 70% trace metal grade HNO3, such that after sample addition, the solution concentration was ~2% HNO3.
Samples were chilled and transported to University of Rhode Island.

Collection of Field Data
Using the pre-installed bladder pumps manufactured by Geotech Environmental (Geotech Environmental Equipment, Inc., 2018) in each well, the waters were pumped into a flow through cell connected to a YSI-556 multiprobe that measures real time changes in chemical parameters observed during pumping. The environmental parameters noted on site were the pH, temperature (°C), conductivity (EC, in mS/cm), dissolved oxygen (DO, in mg/L), and oxidation reduction potential (ORP, in mV, corrected to Eh by addition of 200 mV to the value observed in the field).

Anion and Cation Stock Standard Solutions
Certified

Titration of Samples
Small quantities from each collected sample were used to test for their chloride concentrations using HACH chloride test kit. It was vital that the samples with higher ion concentrations be diluted enough so that all the ions in sample would be in the detection range of the IC instrument.

Calibration standards
The calibration standards for each ion were prepared based upon the chloride concentration levels and the expected high and low detection limits of the ions in the water samples by serially diluting stock solutions for use in constructing the calibration curve in IC and ICP-AES (Table A-1).

Sample preparation
Samples were individually diluted based upon their titration results and their expected ionic detection limits. For IC, samples were diluted as a solution of 1:10, 1:100, 1:1000, or no dilution was done. For ICP-AES, two sets were prepared. Set one contained all the non-diluted samples. Set two was diluted as 1:10, prepared by taking 5mL of sample and adding 45 mL of 2% HNO3 to reach a final volume of 50mL in falcon tubes. Samples were diluted as per the protocol in appendix (Table A-2) and taken to the Brown University laboratory for anion and cation analysis. Samples were allowed to equilibrate to room temperature before analysis.

Procedural Lab Blanks
a) Blank preparation for IC: IC procedural blanks were prepared by taking two 60 mL syringes, filled with deionized water. They were flushed three times, and then, for the fourth time, filled while attached with a Millipore Sterivex syringe-filter (22µm pore size) and emptied into 50 mL falcon tubes. Two falcon tubes were prepared for use as blanks.

b) Blank preparation for ICP-AES:
Two 60 mL syringes were each filled with 20 mL of 2% HNO3. Syringe were covered at end with thumb and rotated to agitate the syringes so that both were all agitated inside with the 2% HNO3. The 2% HNO3 was drained, and procedure was repeated three times. The fourth time, syringes were filled with 50 mL of 2% HNO3.
Two of these were prepared for use as blanks.

Quality Controls
In addition to the standards prepared, the IC and ICP-AES used internal check standards different from the calibration standards. For IC the FAS1, and for ICP-AES QC28 were used, both available from Inorganic Vendors. FAS1 is a 5-anion standard

Dionex Modular DX 500 Ion Chromatography system
The detection of anions (F -, Cl -, SO4 -2 , NO3 -) was done by measuring the conductivity of the separated anions as they eluted from the separation column based upon their affinity with the ion exchange column in the IC. The water samples were analyzed for their anion makeup by the use of Dionex Modular DX 500 Ion Chromatography system at the Brown University, Providence. The samples were prepared as two sets. Set one was non-diluted but filtered for removal of chloride. The samples were filtered for chlorine by running through the Fisher Scientific silver cartridges. Set two was diluted as per the dilution protocol per each sample. The anions present were identified by their retention times, and their quantities were determined by the area of their peaks. The determination of peak parameters (area, height, retention time) was done using Dionex software. The samples were from 9 wells: OCSW, CSW 1-1, CSW 1-2, CSW 1-3, CSW 1-4, CSW 1-5, QV 1-1, QV 1-2, QV 1-3, and two were from a surface water creek site: TC1 and TC2.

Spectrometer system
The well water samples were analyzed for their cation makeup (Ca +2 , Na + , Mg +2 , K + ) by the use of Thermo Scientific iCAP 7400 Duo Inductively Coupled Plasma Atomic Emission Spectrometer system at the Brown University, Providence. An ICP-AES system is made up of two parts: the inductively coupled plasma source, and the atomic emission spectrometry detector. The principal behind the working of ICP AES is the excitation of the samples as electrons, which emit energy at a diagnostic wavelength as they return to their ground states. The emitted energy is characteristic of each element and the intensity of energy is proportional to the concentration of that element. This method identifies the elemental wavelength, and their intensities, the ionic composition can be identified and quantified, relative to a standard. For ICP-AES analysis, the samples were prepared as two sets: Set one was non-diluted. Set two was diluted as 1:10. A total of 11 collected samples were tested for their cation composition, namely Old Core Shed Well (OCSW), Core Shed Wells (CSW 1-1, CSW 1-2, CSW 1-3, CSW 1-4, CSW 1-5), Quarry wells (QV 1-1, QV 1-2, QV 1-3), Temptation Creek (TC1, TC2).

Principal Components Analysis
JMP Statistical Data Analysis Software (JMP version 10) was used to explain key factors and processes controlling the water chemistries at Coast Range Ophiolite.
Water chemistry data and related environmental parameters (with exception of depth) were entered for multivariate statistical analysis and subjected to correlation matrix.
Eigenvalue Pareto Plot, Score Plot, and Loading Plot were generated to extract information on the correlating factors.

Geochemist's Workbench
Geochemist's Workbench (GWB) REACT mode was used to model the low temperature alteration of a serpentinization-influenced water package passing through serpentinite host rock environment. React mode is a program in GWB that models and simulates reactions taking takes in a geochemical system. The REACT mode can trace the evolution of a system as it undergoes reactions in open and closed systems, under various defined conditions.
The conceptual model of the REACT mode simulation is shown in Figure 4 ( Bethke & Yeakel, 2015). An initial system is defined, and then the REACT program calculates the system's initial equilibrium state. The program then simulates a reaction path by adding or removing reactants and adjusting the reaction conditions accordingly. The results are generated as an output dataset and calculations are broken down in a tabular form. REACT works by using the built-in rate laws for different reactions (mineral dissolution and precipitation; aqueous and surface complex dissociation and association; redox; microbially mediated reactions; gas transfers).
The inputs used in GWB modeling are shown in Table 1, Table 2 and Table 3.
Minerals including antigorite, magnetite, greenalite react with four types of input waters (seawater, 10% dilution of seawater, local meteoric water, ultrabasic groundwater). The system is water-dominated, simulating reactions taking place about 1 to 3 meters below land surface at CRO.

RESULTS
The water samples collected at CRO are from nine wells, contextualized by one nearby groundwater-fed alkaline seep (Temptation Creek, TC), from which high elevation (TC1) and low elevation (TC2)  The key environmental parameters collected at CRO are shown in Table 4 Table   5.
The high Ca +2 and Mg +2 concentration values for all the CRO samples can be seen in the Figure 7.
Another notable ionic composition of the CRO waters is their extremely high Na + and Clconcentrations ( Figure 8). The Na + and Clconcentration overload is many times higher than that of the seawater.
When the individual Na + and Clconcentration cross-plot is graphed for the CRO samples and seawater, with the trendline passing through the SW, it can be seen that the Na/Cl ratio is low for QV1-1, CSW1-5, OCSW and high for QV1-3, CSW1-1, whereas the remaining wells QV1-2, CSW1-2, CSW1-3, CSW1-4 appear to be dilutions of seawater as they remain very close on the seawater trendline ( Figure 9). If the increased Na drives these ratios up, there is possible Na desorption from clays or albite dissolution, however if the low Na drives these ratios down, there may be albitization of altered mafic (CSW site) or Na-sorption in the new smectite group clays.
In Figure 9, the OCSW well, shows the most deviation in the Na + and Clcontent from the rest of the wells, being extremely high in Na + as well as in Clconcentrations (Na + =1822ppm, Cl -=4041ppm).
Regarding the ratio of total Na + ion content versus total Clions, all the well samples contain more Clions than Na + ions, which is the case for seawater's Na + and Clcontent. An exception of this is present for the sole well CSW1-1 (Na + =312.8ppm, Cl -=113.6 ppm). Here, Na + concentration is higher than Cl -. The order of wells from most to least is OCSW> CSW1-3> CSW1-5> CSW1-2> QV1-5> QV1-2> QV1-3> CSW1-4> CSW1-1. The briniest OCSW is the deepest well (82m). The least saline is CSW1-1 (the sole well with more Na + than Cl -), and second-from-least-saline CSW1-4 is the shallowest well (8.8m) in the entire set of monitoring wells. The proximity of the CSW1-1 to CSW1-2 is also of interest as not only are the two wells close to each other but are also of very similar depths (CSW1-1=19.5m, CSW1-2=19.2m), yet where the CSW1-2 is the fourth most saline one (with similar Na + /Clratio to that of the seawater), but CSW1-1 is the least saline of all. Overall, the Core  The Eh values range from +418mV (TC1) to -110mV (CSW1-1). Using Garrels and Christ (1965) plot that shows the Eh-pH relation of waters of various natural environments, OCSW, CSW1-1, and CSW1-5 plot at pH of between 10-14, with very negative Eh values, plotting within natural environments that are isolated from the atmosphere. TC1 and TC2 plot around pH 8, with positive Eh values, signalling environments in contact with the atmosphere (Figure 11).
The pH ranges for samples are from 13.5 to 7.6 in the following order: CSW1-1> QV1-1> CSW1-3> OCSW> CSW1-5> QV1-3> QV1-2> CSW1-2> TC2> TC1. The highest pH well CSW1-1 has the lowest Eh value, while the lowest pH site TC1 has the highest Eh value; however, no linearity exists between the other samples. Overall, the ionic concentrations of all the CRO samples, MW and SW show that the CRO samples distinguish themselves from other waters due to their extremely high Na + -Clconcentrations, followed by the high Mg +2 and Ca +2 concentrations. The complete concentration range of all the anions and cations can be seen in Figure 14.
The principal components analysis shows that the first two principal components together account for 64.4% (41+23.4=64.4) of the total variation in the data. The 1 st component (PC1) accounts for 41% of the variation, and the 2 nd component (PC2) accounts for 23.4% of the variation in the data set ( Figure 15).
The Loading Plot shows that if divided vertically into two equal halves, the first and second components in regards to Ca +2 , Mg +2 , K + , and NO3 -. The majority of the clustering is within the quadrant III which shows the negative correlation of 1 st and 2 nd components in regards to their DO and SO4 -2 content. The OCSW is plotted as being the furthest from all the data points (quadrant II). Therefore, the OCSW shows a marginal difference in Na + , Cl -, conductivity, temperature, and pH from all the rest of the water samples. The correlations data table is provided in the ( Table 6).
The GWB software was used to simulate the possible reaction pathways using the input minerals from X-ray diffraction (XRD) profiles of the cores taken from CRO (Cardace et al., 2013) with four types of water inputs (seawater, 10% dilute seawater, local meteoric water, ultrabasic groundwater). The minerals were made to react at three different temperatures (25 0 C, 100 0 C, 2 0 C). The GWB software predicted the changes in pH, Eh, mineralogy, and in fluid chemistry as the serpentine-rich environment reacted with the different waters over a total time span of 100 million years (Ma). The software inputs are listed in Tables 1-3. It should be noted that for the ultrabasic groundwater reacting with serpentine, the system could only proceed to reach completion at the temperature of 25 0 C. Under 100 0 C the residual was too large, and at 2 0 C the initial solution was too supersaturated to proceed.
Changes in pH at 25 0 C: In the case of the seawater reacting with serpentine, there is a small pH increase in the initial 15 Ma (starting from time= 0 Ma), however the system gains a stable pH soon and then stabilizes itself for the rest of the defined time period. In the case of the dilute seawater a very small pH increase occurs in the very beginning, however the pH drops back to the original very soon and stays close to the starting pH for the rest of the time period. The model for meteoric water shows an impressive and sharp increase in pH immediately after the system starts to react. The high pH increase is achieved very quickly within the first few years and shows the most Eh variation over 100 Ma. It decreased to high negative values like the other three models, but unlike the others, the system struggles to gain stabilization.
Even after 100 Ma, the system's redox potential is still changing (Figure 17).
Changes in fluid chemistry at 25 0 C: In the case of the seawater, notable shifts are seen in Al +++ , Fe ++ , H + , SiO2(aq) and  Figure 19).
pH variations among different temperature models: The pH at 25 0 C and 2 0 C for seawater, dilute sea, and meteoric water (no ultrabasic water model present) show very similar patterns. All three types of waters show an initial increase in pH (dilute seawater pH drops down after the initial increase).
However, the pH model at 100 0 C show decreasing pH values for seawater and dilute seawater. In the case of the meteoric water model at 100 0 C, it shows the same pH increase as seen in meteoric waters at 25 0 C and 2 0 C temperatures (Figure 16, 20,21).
Eh variations among different temperature models: Like the pH patterns, the Eh at 25 0 C and 2 0 C for seawater, dilute sea, and meteoric Fluid chemistry variations among different temperature models: Like pH and Eh, the seawaters and the meteoric waters at 25 0 C and 2 0 C show similarities as the same ions undergo changes in similar ways, for both temperature models. The dilute seawater models for 25 0 C and 2 0 C are also similar to each other.
However, at 100 0 C, the seawater shows a different water chemistry with HCO3and H + leaching into the waters, and Al +++ with an initial increase and then stabilizing. The meteoric water at 100 0 C also behaved differently than that of other temperature models. SO4 -concentrations remain higher in this model, and unlike the absence of H + under 25 0 C and 2 0 C, here H + is produced after 70 Ma (Figure 18, 24, 25).

DISCUSSION
The process of serpentinization leads to the formation of waters that are extremely rare in the natural environments (Neal, 1984;Chavagnac et al., 2013). The physical and chemical data from CRO shows the presence of Type I and Type II waters at CRO. The Ca/Mg ratios show that TC1, TC2 and CSW1-4 are Type I (high Mg +2 ) open system waters. OCSW, CSW1-1, CSW1-3, and QV1-1 are the Type II (high Ca +2 ) closed system water. CSW1-2, CSW1-5, QV1-2, and QV1-3 are found to be the intermediate, mixed water ( Figure 28). CSW1-4, the shallowest of all the wells, is an open water system, unlike any other groundwater wells. High pH, high Ca +2 -OHwaters, and lower pH, high Mg +2 -HCO3waters are unique to serpentinizing sites (Barnes and O'Neil, 1969;Paukert et al., 2012).
All the samples show high Na + and Clconcentrations. This is due to the reaction of Cretaceous seawater trapped within the ophiolite during its emplacement and reacting with the surrounding rocks (Peter, 1993;Schulte, 2006). The stable isotope data from CRO also supports presence of seawater as the serpentinizing fluid (Barnes et al., 2013). The OCSW shows the greatest Na + and Clconcentration due to being the deepest with more surface area for interacting with altered fluids and bedrock constituents. CSW1-2, CSW1-3, CSW1-4, and QV1-2 show similar Na + and Clratios as that of sea water, therefore they appear to be dilutions of varying extent of the trapped sea waters. These dilutions of SW can be due to the influx of meteoric and other shallowly sourced waters.
All the well samples maintain the same Cl -> Na + content as in seawater, with the exception of CSW1-1. CSW wells are brinier than the QV wells. Despite the close proximity of all the CSW wells to each other, CSW 1-1 is least saline of all the wells, including the QV wells. One of the possible explanation that puts CSW1-1 apart from others might be a result of casing. All the wells except for CSW1-1 and QV1-1 were cased with PVC pipes. The CSW1-1 and QV1-1 are also larger in diameter than the other pipes (Twing et al., 2017).
Temperature profile of the wells show variations that are irrespective of the depth.
The subtle temperature variations noted here are seasonal and site-specific (related to heat from solar radiation striking the land surface, conducted to some depth below the land surface), or in-flow of regional geothermal waters. Using Garrels and Christ's Eh-pH plot for finding the limits of the naturally occurring aqueous environments, OCSW, CSW1-1, and CSW1-5 show stability range within environments that are bedrock-water interactions for the wells and spring waters, is proposed in Figure 30.
GWB software was used to predict the changes that took place over the 100 Ma time frame, using four kinds of input waters (seawater, 10% dilute seawater, meteoric water, ultrabasic groundwater) and under three different temperature settings (2 O C, 25 O C, 100 O C). The GWB software showed no effect of temperature for 2 O C and 25 O C. In both models, the pH increases sharply for meteoric water, gradually for seawater, and a very small change in the case of dilute seawater. This is consistent with the observed high alkaline pH values for CRO as well as other known serpentinizing site. Similarly, the results for Eh showed no effect of temperature over Eh changes. All kinds of water, at all three temperatures, showed the decreasing (high negative) Eh values which are consistent with extremely reducing waters as observed in field at CRO and other serpentinizing sites. The software also showed leaching of minerals in and out of the water as it flows through the bedrock, with corresponding mineralogical changes in the serpentine rich environment. Leaching of the ultramafic rocks into the reacting waters is considered to be influenced by the chemical properties of water, the temperature, pressure, and the chloride content (Moody, 1976). The models for all the waters show that the leaching is lowest for 2 O C, with an increase for 25 O C, and the most leaching taking place at 100 O C. Study on Oman and Ligurian ophiolites show that the fluid compositions vary among one ophiolite to another, and also within the same ophiolite (Chavagnac et al., 2013).
The main ions that take place in noticeable chemical changes in waters are Al +++ ,  (Moody, 1976). Numerous smectites, phyllosilicates, inosilicates are formed. Al +++ concentrations in fluids are explained by the emergence of albites (saponite-Na, muscovite, annite, gibbsite). This also provides the answer to the observed Na/Cl ratios in the CRO groundwaters ( Figure 9). GWB modeling suggests that it must be the low Na that drove the Na/Cl ratio down due to albitization of altered mafic and/or  (Morris et al., 2010) and OMEGA (Observatoire pour la Mine´ralogie, l'Eau, les Glaces, et l'Activite) (Bibring, et al., 2005). Along with the smectite clay minerals, kaolinites have also been found at Mars (Baumeister et al., 2011 Type II).
Also, FeO(c) formation is limited to highly reducing environment (highly alkaline, Type II). This is supported by the findings that Mg is completely depleted in waters of pH 10.5 and higher, whereas Ca ++ accumulates with pH increase (Chavagnac, 2013).
Among all the GWB models, the most difficult model to predict fluid composition accuracy would be in the case of meteoric model because meteoric waters undergo unpredictable compositional changes during runoff.

CONCLUSION AND FUTURE WORK SUGGESTIONS
The Coast Range Ophiolite can be considered a site of ongoing low temperature serpentinization, with weathering related processes at work evidenced by environmental and geochemical parameters (redox measurements, temperature, pH, electrical conductivity, ionic composition). Physical parameters highlight that these high pH and low Eh groundwaters fall into known ranges for serpentinizing systems.           Figure 11. Based on the classic Eh-pH ranges for natural environments (Garrels and Christ,1965), OCSW, CSW1-1, and CSW1-5 show strongly reducing values (environment isolated from atmosphere), whereas TC1 and TC2 show oxidizing values for environments in contact with the atmosphere.                      Table 2: Ionic composition of regional precipitation (MW) at Menlo Park, California, from 1957-1959(from Berner & Berner, 1987.
Ionic composition of regional precipitation at Menlo Park, California (1957California ( -1959