Honours Thesis Abstract
ARSENIC CONTAMINATION IN THE SUNDOWN-JIBBINBAR AREA,
SOUTHEAST QUEENSLAND
Megan Packer
UQ,Qld
2004 AIG Honours Bursary Winner
This research investigated water arsenic and sediment leached arsenic in two major
river catchments draining the Sundown-Jibbinbar area, the Pike Creek and the Severn
River. The Sundown-Jibbinbar area of the New England Province is naturally high in
arsenic, several abandoned arsenic mining operations and naturally exposed arsenicbearing mineralisation pose as possible major point contamination sources. However,
their influences on arsenic levels at regional scales were unknown, and regional
baseline levels had not been previously determined.
In order to identify pollution inputs, arsenic trends were correlated with lithological
data as well as locations of historical mining activities. Methods used to accomplish
these objectives included detailed geological mapping of the area surrounding the
Jibbinbar State Arsenic Mine, to determine lithological and structural relationships
with arsenic-bearing mineralisation. This was an attempt to produce a predictive
model of mineralisation distribution on a more regional scale. Field investigations
concentrated on locating lithological contacts, measuring structural fabrics and
identifying facies variations within units. This was achieved from comprehensive
rock sample and thin section analyses, representing all units and facies in the
Jibbinbar area. Mineralogical, textural and structural properties were identified for all
units in terms of characterising different granite and hornfel facies.
The most prominent observation was the significantly reduced extent of the Ruby
Creek Granite exposure compared to existing mapped boundaries. Smaller, felsic
granite outcrops neighbouring the Jibbinbar State Arsenic Mine were not
characterised by the features of the main pluton body which forms Mt Jibbinbar.
These quartz-feldspar porphyry aplite facies were distinguished from the
hypidiomorphic-granular textured pink, equigranular to aphanitic-porphyritic Ruby
Creek Granite by its predominantly recrystallised and phaneritic texture and more
felsic modal assemblage. Fractures and vein quartz structural trends control drainage
patterns and correlate to the Severn River Fracture Zone and conjugate fractures
striking north-northwest. Structurally controlled arsenic-bearing mineralisation does
not appear to have specific relationships with lithologies. Structural control is very
important in the distribution of mineralisation lodes, however, the lack of any
correlation with lithology limits the ability to accurately predict arsenic-bearing
mineralisation occurrence and extent in the Sundown-Jibbinbar area.
A comprehensive water and sediment survey was conducted over the Pike Creek and
Severn River catchments. Water samples were analysed for a complete suite of
elements using ICP-MS. Sediments were exposed to a mild acetic acid leaching
procedure before being analysed using ICP-MS. Sediment properties were also
characterised by grain size fractions, composition and organic matter using a LOI
technique. Water and sediment arsenic trends in the two catchments were strongly
correlated and baseline arsenic levels were well below ANZECC guidelines. Elevated
values were noted in neighbouring areas downstream of the Jibbinbar State Arsenic
Mine and the Sundown mines. These values supported previously determined high
arsenic levels at these specific sites. One area of concern was identified due to its
high arsenic but low copper and iron values, indicating a possible waste dumping site.
No relationship with lithology was observed and thus, these catchment-specific trends
cannot be applied to a broader New England Province scale.
Natural arsenic baseline levels in the Pike Creek and Severn River catchments display
trends of arsenic inputs and subsequent dilution and buffering as a function of
distance downstream from the point contribution site. Total arsenic for all SundownJibbinbar collected sediments have not yet been determined, however, initial runs
show higher values than the non-mineralised Brisbane River catchment, southeast
Queensland. Moderately polluted sediments in this catchment are resultant from
arsenic emissions from industries including petroleum refineries, aeroplanes and
electricity generation operations which contribute substantial quantities of arsenic into
the environment. Although total arsenic levels in sediments may be high, the
bioavailable fraction released under natural conditions and water arsenic levels
suggest that arsenic pollution does not pose an ecological or health threat in the
Sundown-Jibbinbar area.
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