A consultation into plans to mine the seabed off the Cornish coast ends this week.
The multi-million pound proposal by Marine Minerals Limited would see the sea bed searched for tin, washed down over decades from Cornwall's mines.
Protestors say the plans could cause environmental damage, and put off tourists.
The company says the mining could bring much needed jobs and would only go ahead if "stringent commercial, environmental and social requirements" can be satisfied.
The scheme would see the Cornish company carry out exploratory drilling on parts of the seabed from St Ives bay to Perranporth.
Among the concerns are the mining's impact on important grey seal habitats
Christopher Davies, a spokesman for Marine Minerals Limited, said: "We're a Cornish company so we want to know can this be done in a way that is environmentally acceptable and practical.
"We think it can but we want to do our proper environmental study to look at the factors that could be affected. We have rejected utterly the idea of it being traditional dredging. It needs to be a much more careful process."