Understanding Fluid-Rock Interactions: An Interview with Pooja Sheevam, Part IV

In Part III of our interview with Pooja Sheevam it focused on the use of long-wave IR (LWIR) spectroscopy in analyzing basaltic rocks, particularly between 5–15 µm (1,2). Sheevam highlighted how her team used LWIR to identify primary silicate minerals like pyroxenes, olivines, and feldspars, which are challenging with shortwave techniques (1,2).

In Part IV of our conversation with Sheevam, she discusses how scanning electron microscopy with an energy-dispersive X-ray spectroscopy (SEM-EDS) and bulk X-ray fluorescence (XRF) were used to better understand fluid-rock interactions.

Will Wetzel: What advantages did SEM-EDS and bulk XRF geochemical analysis bring to the study, particularly in understanding fluid-rock interactions?

Pooja Sheevam: When I say SEM-EDS, I'm basically talking about the scanning electron microscopy, which has an energy dispersive X-ray, which is just the way the electrons are hitting the surface. SEM was critical not only for validating the mineral end members identified in our spectral analysis, which we also got from X-ray diffraction (XRD), but also for visualizing textures that aren't obvious in hand samples. There’s only so much magnification a magnifying glass can do, whereas SEM goes in scales of 10–1000 times magnification. While in the SEM, the validating mineral end members weren't necessarily needed because we were very confident with our spectral results, and they were very clear. But I think that visualizing the textures was a cool thing to see in alteration features and localities. In mining, a lot of times, they really look for specific mineral phases in the alteration textures, which is hard to see without magnification. So that's how it added value to our study.

We performed the destructive lab XRF, where we sent the samples in. It's almost like the acronym is inductively coupled plasma-mass spectrometry (ICP-MS) or inductively coupled plasma-atomic emission spectroscopy (ICP-AES), where they quite literally burn the rock and obliterate it. But what that helped us do is evaluate elemental mobility across the core. So we weren't getting mineral speciation; we just wanted to look at the elements themselves. So XRF allowed us to trace that fluid-rock interaction indirectly, even though it doesn't provide a rate of fine-scale speciation. So together, these methods really added depth to our understanding. And really, when you're dealing with extensive, acidic, or even boiling water, you get very specific textures. You get very specific elements that are being mobilized. And so those methods help you tease out what that looks like.

This interview with Sheevam is the fourth part of a five-part interview series. You can watch the previous segments of our interview with Sheevam below.

Part I

Part II

Part III

References

1. Sheevam, P.; Calvin, W. M. Comprehensive characterization and geochemical alteration pathways of drill core from the Humu'ula Groundwater Research Project, Hawaii, USA: I. Pohakuloa Training Area. J. Vol. Geo. Res. 2025, 462, 108311. DOI: 10.1016/j.jvolgeores.2025.108311
2. Wetzel, W. Quantifying Mineral Phases in Shield Basalts: An Interview with Pooja Sheevam. Spectroscopy. Available at: https://www.spectroscopyonline.com/view/quantifying-mineral-phases-in-shield-basalts-an-interview-with-pooja-sheevam (accessed 2025-06-03).