the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 01 Apr 2026
Fault and fracture networks as long-lived conduits for lithium transport
Abstract. Lithium brine systems are critical resources for the energy transition, yet the mechanisms governing lithium mobilization, transport, and concentration remain poorly constrained. In particular, the role of fault and fracture networks in controlling fluid flow and lithium distribution is not well resolved. Here we investigate the structural controls on lithium transport in Clayton Valley, Nevada, a key lithium-producing basin in the USA. We present new analyses of calcite-mineralized faults, opening-mode fractures, and spring deposits that record lithium-bearing fluid flow over >10 Myr of Basin and Range extension. Hereafter, opening-mode fractures are referred to as “fractures,” and mineral-cemented faults or fractures as “veins.” Calcite U–Pb ages (15–4 Ma), clumped-isotope formation temperatures (25–140 °C), and lithium concentrations (up to 460 ppm) demonstrate that fault and fracture networks repeatedly transported lithium-bearing fluids through basement, along basin margins, and within basin fill throughout basin evolution. Lithium concentrations vary systematically with host setting, with the highest values recorded in basin-fill-hosted veins and spring deposits and generally lower values in basement-hosted and basin-bounding fault veins. Several lithium-bearing calcite veins yield U–Pb ages that predate emplacement of late Miocene silicic volcanic units by up to ~9 Myr, demonstrating that structurally focused lithium transport occurred prior to emplacement of widely cited volcanic source reservoirs. Temperature and stable isotope constraints indicate dominantly meteoric fluids advected to depth and focused along faults, suggesting that lithium transport and enrichment in Clayton Valley does not necessarily require ascent of lithium-enriched magmatic fluids along deeply rooted crustal-scale faults. These results show that long-lived fault and fracture networks act as persistent pathways for lithium transport and redistribution within closed extensional basins. Although fault-controlled lithium enrichment has been recognized previously, this study provides direct evidence for structurally focused lithium transport over multi-Myr timescales.
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Status: open (until 15 May 2026)
- RC1: 'Comment on egusphere-2026-1596', Michael Darin, 01 May 2026 reply
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RC2: 'Comment on egusphere-2026-1596', Fabrizio Balsamo, 15 May 2026
reply
Dear Editor,
This is my review of the paper Fault and fracture networks as long-lived conduits for lithium transport, by Cawood and coauthors.
The manuscript presents a multi-disciplinary dataset (field observations, U–Pb calcite geochronology, clumped isotopes, and lithium concentrations) to investigate the role of fault and fracture networks in lithium transport in Clayton Valley, Nevada. The study addresses an important question in the context of lithium brine systems and provides valuable new geochemical constraints on structurally controlled fluid flow in continental settings.
The dataset is novel and potentially significant, particularly the integration of absolute timing of vein formation with lithium geochemistry. The text is clear, terminology is correct, and figures are adequate, self-explicative and very beautiful. The comparison with literature is sound, and the overall dataset is certainly worth to be published.
However, in my view (structural geology perspective) there are three main aspects that require clarification or additional support. These concern with overall structural characterization of faults, petrographic and microstructural control on U-Pb ages, and source of lithium. Below more detailed comments.
In summary, this manuscript presents a valuable and potentially publishable dataset, but the interpretations would be substantially strengthened by a more rigorous integration of petrography, structural geology, and fluid-source discussion. I believe the paper has strong potential after revision and I therefore recommend moderate revision.
Best regards
Fabrizio Balsamo
Major points to be addressed:
- Petrographic characterization and vein microstructures
One of the main weaknesses of the manuscript is the absence of a general petrographic and microstructural characterization of the sampled veins. The paper repeatedly emphasizes the role of fault and fracture networks as long-lived conduits for lithium-bearing fluids, yet the evidence presented is almost entirely based on field observations and bulk geochemical analyses. In a contribution centered on structural controls on fluid circulation, this leaves an important gap in the overall argument.
At present, the manuscript does not provide sufficient information regarding the internal textures of the calcite veins, the relationships between different generations of calcite, or the deformation mechanisms associated with vein formation (opening-mode, shear veins?). There is little discussion of whether the veins formed during active deformation, whether they record repeated opening and sealing events, or whether multiple mineralization phases are present within individual structures. Likewise, the manuscript does not address the occurrence of crack-seal textures, recrystallization fabrics, brecciation, possible cross-cutting relationships, or evidence for vein reactivation. These observations are essential because they provide the direct structural context needed to interpret the veins as long-lived pathways for episodic fluid circulation through time (even at the scale of individual veins).
This issue becomes particularly important given that the manuscript interprets the calcite mineralization as recording repeated lithium-bearing fluid flow over multi-million-year timescales. Without petrographic evidence demonstrating multiple generations of vein growth or reactivation, it remains difficult to evaluate whether the analyzed calcites represent discrete mineralization events or composite vein histories that potentially integrate multiple fluid-flow episodes.
I strongly encourage the authors to include a dedicated section describing the petrography and microstructures of the sampled veins. Representative thin-section images, accompanied by descriptions of vein fabrics and paragenetic relationships, would substantially strengthen the manuscript. Such observations would also help clarify the temporal and structural relationships between deformation, vein formation, and fluid circulation, thereby reinforcing the broader interpretations developed in the Discussion.
- Structural characterization/description of the fault systems
A second major limitation of the manuscript is the lack of quantitative structural characterization of the studied faults, particularly the basin-bounding structures that form the basis for several of the paper’s conceptual interpretations. Although the manuscript frequently refers to “faults,” “fracture networks,” and “basin-bounding faults,” the actual geometry, scale, and internal architecture of these structures remain poorly constrained throughout the paper.
For example, the manuscript does not provide sufficient information regarding the displacement of the major faults, the thickness of the fault cores, the width of associated damage zones, or the intensity and distribution of fracturing adjacent to the principal slip surfaces. These details (even qualitative description) are fundamental in any study addressing structurally controlled permeability because the hydraulic behavior of fault systems varies significantly depending on structural attributes (in broad sense) and position within the fault architecture (i.e. wall damage zone, tip damage zone, intersecting damage zone, following recent classifications…).
At present, it is unclear where the analyzed samples were collected relative to the structural architecture of the faults. The manuscript should clarify whether the calcite samples derive from the principal slip surface, brecciated fault-core material, subsidiary fractures within the damage zone, or fractures external to the fault zone altogether. Similarly, there is little quantitative description of the sampled veins themselves, including their thickness, continuity, orientation.
These structural details are critical because the manuscript ultimately argues that faults acted as long-lived pathways organizing lithium transport through the basin. Without a more rigorous structural framework, it is difficult to assess the extent to which the analyzed veins genuinely record basin-scale fault-controlled flow as opposed to more localized fracture-related circulation.
I therefore recommend that the authors expand the structural description substantially. The paper would benefit greatly from a more detailed description of the principal faults and fracture systems, including quantitative parameters where possible, together with clearer documentation of sampling positions relative to fault zone structure and map view architecture.
- Source of lithium and implications for basin evolution
The discussion regarding the origin of lithium is one of the most interesting aspects of the manuscript, but it is currently underdeveloped relative to the importance of the conclusions being proposed. A central claim of the paper is that several lithium-bearing calcite veins predate emplacement of the late Miocene silicic volcanic units commonly invoked as the principal lithium source in Clayton Valley. This observation is potentially significant because it suggests that lithium-bearing fluids were already circulating within the evolving basin prior to the emplacement of the volcanic units typically considered critical to lithium enrichment.
However, while the manuscript questions the conventional volcanogenic source model, it does not sufficiently develop alternative explanations for the origin of the lithium. The current discussion largely demonstrates that lithium transport occurred before the emplacement of certain volcanic units, but it does not clearly establish where the lithium was sourced from during these earlier stages of basin evolution. As a result, the interpretation remains somewhat incomplete and, at times, speculative.
The manuscript would benefit from a broader and more balanced discussion of possible lithium reservoirs and mobilization mechanisms. For example, the potential role of basement lithologies, earlier volcanic sequences, sedimentary recycling, long-lived regional groundwater circulation, or inherited basin fluids deserves more careful consideration. Likewise, the extent to which the presented geochemical and isotopic data can actually discriminate among these possible sources should be discussed more explicitly.
This point is particularly important because the manuscript presently risks overextending the implications of the geochronological dataset. Demonstrating that lithium-bearing fluids predate a specific volcanic event is not necessarily equivalent to demonstrating that volcanism was unimportant in the overall lithium budget of the basin. The authors should therefore clarify the distinction between evidence for early lithium circulation and evidence for the ultimate lithium source itself.
A more nuanced treatment of lithium sourcing would considerably strengthen the manuscript and place the results in a broader basin-evolution and fluid-flow context.
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- 1
GENERAL COMMENTS:
The manuscript presents new calcite U-Pb geochronologic ages, carbonate clumped-isotope formation temperatures, and lithium concentration data from fault- and fracture-hosted veins, basin-bounding faults, and spring deposits in and around Clayton Valley, a prominent and developing lithium district in southwestern Nevada. The authors interpret these data as evidence that structurally connected fault networks served as long-lived conduits for Li-enriched fluid flow since at least ~15 Ma, predating the emplacement of the ~6 Ma Rhyolite Ridge tuff which has been suggested as a primary Li source reservoir for the Clayton Valley system. The paper addresses a genuinely important and underexplored question: the role of faults and fractures as fluid transport pathways in sediment-hosted Li and Li-brine systems is poorly constrained, and the multi-proxy analytical approach employed here is well suited to the problem. The topic is within scope, and the dataset is novel.
Unfortunately, the manuscript falls well short of supporting its central conclusions, and in its current form I do not recommend it for publication without major revision. My principal concerns are as follows. The paper's most significant interpretive claim – that Li-enriched fluids were circulating along faults prior to 6 Ma, before establishment of the volcanic Li source – is not supported by the data. All fault calcite samples with robustly pre-6 Ma U-Pb ages yield Li concentrations of only 2–21 ppm, at or below average upper continental crust (~35 ± 11 ppm; Teng et al., 2004), providing no geochemical evidence of Li enrichment. Compounding this, the manuscript does not discuss the 2σ uncertainties on U-Pb dates, which are substantial: eight of thirteen dated samples have age uncertainties large enough to overlap the 6.05 Ma age of the Rhyolite Ridge tuff, and cannot be used to argue for pre-source fluid flow. The authors' conclusion that long-lived, pre-volcanic Li transport occurred within the basin is therefore unsupported, and represents a significant overinterpretation of the available data.
The manuscript also contains errors in the representation of average upper continental crust Li content. They cite inconsistent values (~20-30 ppm and 8.5–11.5 ppm in Fig. 3a; ~30 ppm in text) that are neither internally consistent nor traceable to the cited source, which further undermine the interpretive framework. The correct reference value from Teng et al. (2004) renders the statement that "many samples yield Li concentrations that exceed average upper continental crust" incorrect for the majority of the dataset.
Beyond the geochemical interpretations, the petrographic characterization of dated calcite is insufficiently documented to establish that U-Pb ages reflect fault-controlled fluid flow rather than diagenetic, recrystallized, or mixed-generation calcite. CL imaging and textural descriptions linking each sample to its structural position are absent, which is a meaningful gap given current best practices in fault calcite U-Pb geochronology.
The structural figures (Figs. 1, 5, and 8) contain geometric and stratigraphic errors inconsistent with published mapping and structural analyses of the region, including incorrect crustal thickness at Mineral Ridge and Rhyolite Ridge, omission of key SE-dipping fault structures, erroneous detachment timing, and the conspicuous absence of the Rhyolite Ridge tuff from beneath Clayton Valley — despite its documented subsurface occurrence in work by several coauthors. These figures require substantial revision and should be explicitly labeled as conceptual or schematic where appropriate.
More broadly, the discussion is insufficiently developed to support the claims made. The significance of results is overstated and engagement with the existing structural and stratigraphic literature is incomplete. Addressing these issues – particularly the Li content interpretation, age uncertainty treatment, petrographic documentation, and structural figures – would require substantive revision but could yield a much stronger contribution.
Specific Comments and Technical Corrections can be found in the PDF supplement.