Oct 16 (Reuters) - Rio Tinto reported a

1% rise in third-quarter iron ore shipments on Wednesday, but

marginally missed market expectations, as operational

improvements at its Pilbara operations lifted output.

Iron ore prices remained under pressure for the larger part

of the third quarter due to dimmed demand prospects in top

consumer China's steel market amid persistently weak property

prices.

The world's largest producer of iron ore shipped 84.5

million tonnes (Mt) of the steel-making commodity from its

Pilbara operations in the three months ended Sept. 30, compared

with 83.9 Mt a year earlier.

That compares with a Visible Alpha consensus estimate of

84.74 Mt.

Shipments improved from a June quarter marred by low

portside inventories and the impact of a train collision.

Pilbara iron ore production in the three months ended

September was 84.1 Mt, compared with 83.5 Mt a year earlier.

Rio, which recently agreed to buy Arcadium Lithium ( ARLTF )

for $6.7 billion in a deal that will make it the world's third

largest miner of the battery metal, reaffirmed its 2024 Pilbara

iron ore shipments forecast of between 323 Mt and 338 Mt.

The company said unit cash costs for Pilbara iron ore for

the year would be at the upper half of its $21.75 to $23.50 per

tonne forecast, reflecting higher inflation expectations.