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The
Taan iron deposit is a sedimentary bog
iron consisting of an upper layer of
crispy limonite with floral imprints
which grade down to limonite and poorly
sorted
limonitic conglomerate. The deposit lies
unconformably above the truncated
surface
of a metamorphosed sequence of volcanic
flows and clastic rocks and forms a
mantle
fringing the slopes within the watershed
of the Taan River.
Geomorphic indications together with
features of the deposit seemingly
indicate
that iron deposition took place in a
ponded drainage basin developed as a
consequence
of t.he down-faulting of the headwater
portion of the former San Juan River.
The
iron have probably been derived from the
weathering of pyritic rocks and volcanic
rocks within the neighborhood of the
present day deposit, taken in solution
and trans-
ported by streams and slope wash into
the basin, possibly both as ferrous and
ferric
ions. The iron ions were later further
oxidized, precipitated and settled in
areas free
of currents and thereon lithified to
form the present deposit. |
