by Leah Lynham, James Cook University
Palaeochannels: Most geologists working in the Eastern Goldfields will have explored them and most prospectors will have found gold in them. Many old timers would have followed deep leads leading to riches that turned out to be palaeochannels (such as Kanowna). But is gold all they’re good for? Absolutely not.
As a palaeochannel researcher, I am often dismayed at how little exploration geologists know about the rich and diverse palaeoenvironmental history contained within palaeochannels of the Eastern Goldfields. Drowned forests, marine transgressions (yes, more than one), macro and microfossils and a rich rainforest palynoflora are all present, spanning just 30 million years of geological time. Imagine, a rainforest where red dirt dominates the Kalgoorlie landscape today.
Wildest Dreams
How did a girl from London used to 24/7 conveniences pack up her bags to move to an outback mining town to call home to research the microfossils of an ancient drainage that once coursed underneath the streets and houses? David Attenborough. And a very nonlinear path.
I credit David with my career. When I was a child I watched his documentary, ‘Lost Worlds Vanished Lives’ which inspired me to become a palaeontologist. I used to use my Lego to build my own prehistoric worlds. In my teen years, in a low socioeconomic area, I buried the dream. Palaeontology was a career for other people, not girls that needed to work full-time as soon as they left school. But, with some sheer determination (and chronic sleep deprivation) I managed to get to college where I did study geology. But that was a complete accident. I thought gemstones were pretty, so ended up in a geology A-Level. I quickly fell in love with the subject realising that I could actually make a career of this. I went on to read geology at the University of Plymouth where I had several amazing lecturers who encouraged my love of palaeontology and palaeoenvironment. Even the structural geologists knew it was a lost cause trying to get me over to their side when I used graptolites in a structural exam as evidence for the closure of the Iapetus Ocean and suture development. I developed a passion for marine micropalaeontology and benthic foraminifera in my second year and went on to specialize in biostratigraphy for oil and gas exploration, tailoring my MGeol year to all things palaeoenvironment. I was lucky enough to work with Fugro Robertson on North Sea Oil and Gas samples.
Then I moved to Australia, and there is not much opportunity for a benthic foraminifera biostratigrapher out here, so I packed my dream away and went into exploration. For a few years I worked on a range of commodities including Au, Fe and Li but my passion for palaeontology never left. Coming off maternity leave, my husband’s then boss asked me if I wanted to see some fossils they had pulled out of an open pit, and truth be told I thought he had been in the sun too long. Fossils in a gold mine on the Yilgarn? But there they were, a block of marine bivalves (Figure 1). This got me excited and after a lot of emails back and forth between the mining company, myself and JCU, a PhD research project was formed. I found myself in a niche little world I’ve continued to carve for myself, a regolith geologist straddling both industry and academia, using the palaeoenvironment to assist palaeochannel exploration activities.
Everything has changed
Enough about me, what geological riches has my research found? Logging over a hundred drill holes, both diamond and RC, newly discovered outcrops and pit wall exposures, it’s clear that the stratigraphy is not as simple as the current model shows. We do not have the basic layered package of gravel, clay, lignite, spicules. Every environment interfingers with another spatially across the Lefroy Drainage, making for a very confused-looking attempt at a 3D model, but this does give us further insights into palaeocurrent directions and the timing and separation of the Lefroy and Cowan drainage systems.
Two clear catchments are seen in the basal Au producing gravel, one the standard quartz gravel well known throughout the Goldfields, but a second smaller source catchment consisting of immature polymictic conglomerate also exists and may indicate more than one provenance of basal placer deposit. Muds associated with the polymictic layer have been dated in collaboration with MGPalaeo (a Perth-based geological and stratigraphical consultancy specializing in palynology) and give us the same N. asperus zone, as the quartz gravel so we know they were deposited at the same time.
Thanks to my Industry Partner Gold Fields and their St Ives Mine Site I’ve been able to join their geologists in visiting open pit sections of palaeochannel and through this discovered a drowned forest-type environment in the Werrilup Formation, something previously seen in the Cowan Drainage system, but not reported on from the Lefroy. It’s incredible to look up at a pit wall and see clear columns of lignitic material, flooded by fine grained clays, giving a wonderful insight into what it would have been like in Kambalda ~35Ma. We would have been standing in a vast anastomosing river valley, in a temperate rainforest, with lazy water ways. There has not been any evidence of terrestrial fauna but I hold out hope that it will be found.
Along with these new discoveries come insights of onshore material, for the first time a clastic shallow marine interval, equivalent to the Pallinup Formation has been described. This is an earlier unit, representing the Tuketja Transgression, and the change from swampy clays and lignite deposited in an anastomosing river environment, to a widespread shallow sea, reaching far in-land, in what we have deemed the ‘on-shore’ Eucla Basin. This is the unit that sparked my research. When viewed underneath a microscope it is surprisingly full of microfossils. It turns out these microfossils (Figure 2) have never been described from the Yilgarn before, and I am identifying them ready to share them with the world. The deposition of this clastic material was followed by deposition of the well-known marine Princess Royal Spongelite member of the Pallinup Formation. But sponge body fossils were not known from the Lefroy drainage system, as it was previously believed to be a marginal marine, high energy environment. New field locations from this research have discovered a shallow water sponge reef (Figure 3), covering a couple of hundred meters across and around 3 m (9.8 ft) high, much further inland than previous shorelines have been placed. Many of the species are believed to be novel to science, and a collaboration with palaeontologists in Poland will bring this information to life.
Fieldwork in previously under-explored areas of the lower reaches of the Lefroy Drainage System have revealed extensive new outcrops of sponge body bearing spiculitic sediments, extensively bioturbated spiculitic sands, and even a few outcrops of fluvio-glacial material. This may help define exactly when these large-scale drainages traversing the Yilgarn were incised. I have even found a coccolithophore (a calcareous nannofossil and type of phytoplankton) accidentally when analysing legacy material under the SEM (Figure 4), and I am almost 100% confident it’s the first coccolithophore ever seen from the Yilgarn. I do not doubt that continued exploration of the buried drainages of the Yilgarn will discover more treasures just waiting to be described.
Long story short
The knowledge gained throughout my PhD research isn’t just an insight into the Eocene environment of Western Australia. Nor just a potential useful vector for gold exploration by using palaeoenvironmental knowledge to hopefully predict where the next big placer gold deposit will be found. My favorite use is getting children excited about earth sciences.
My main passion lies with educating tomorrow’s earth scientists. I bring tangible evidence of changing landscapes from where they live into the classroom. I have worked with many schools across Western Australia, creating incursions and excursions for students from Kindergarten to Year 12. Fossils are highly engaging and capture the attention of all students and foster interest in the changing world they live in. Show students a 35-million-year-old marine gastropod shell and ask them what they think it is. They all say ‘seashell’, and then you tell them it was found just 15 km (9.3 mi) away in the very open pit many of their parents work, in the middle of a red dirt desert and you have captured their attention and imagination.
‘Really, Miss? A seashell? But there’s no ocean here.’
‘There isn’t,’ I’ll reply, ‘but there used to be.’
Then begins my spiel about diverse and changing landscapes and natural history (Figure 5). I paint a picture of how Kambalda and Kalgoorlie were once covered in a shallow ocean filled with marine life. How where we stand today was at one stage a rainforest and of course how geology really should be considered a career. After all, the students live here every day exposed to the outdoor classroom; this exposure and accidental knowledge will be a major advantage should they pursue a career in earth science. I often take school groups to Mount Hunt, a location many geologists in the area are familiar with as it contains evidence of a much older sea floor in the form of 2.6 Ga Paringa Basalt pillow lavas. This site expands their concept of where we live and understanding of geological time. They are surrounded by tangible evidence for deep geological time and the repeating cycle of land and oceans on the planet. This is also a good time to whip out the toothpaste experiment for pillow lava formation.
My approach to educating the next generation is not without difficulty. Many mining companies simply do not appreciate the rich geological heritage of the 30-100 m (98-328 ft) of stratigraphy overlying basal palaeochannel gold. It is the overburden to be stripped away and dumped. However, as I have discovered that overlying stratigraphy is filled with novel fossils and knowledge and has become the perfect vehicle for getting the next generation involved in Earth Sciences. I have made it my one-woman mission to spread the good word of the middle-late Eocene palaeoenvironment of the Eastern Goldfields, but also to stress how it can be useful in determining potential locations for palaeochannel deposits. As my parting words, I am going to implore mining companies to save their RC chips, to save some diamond core of channels, photograph it like you would your hard rock, both wet and dry, and extra images of interesting features, and teach your geologists how to log it properly. We have lost so much knowledge due to poor logging and disinterest in geological knowledge for knowledge’s sake. The mine I’m working with for my research has been exploiting palaeochannel gold for over 30 years, but the presence of microfossils had not been documented until I looked at some of the Neptune open pit marginal marine sediments under my microscope. How much information have we lost over the years?
And with that my final words. We need fresh minds if Australia wants to continue to be a resource powerhouse and to find fresh minds, Earth Science communication is all of our responsibility. Save a sample, talk to a child, share a post, or sponsor a book for a local library. Keep our field thriving for decades to come.
