If you look carefully at the big grille, I think that's a waterwheel chamber and the duct to it is the tunnel which has half fallen away in the cliff. (we were going to ab off the cliff into this but it probably goes to a collapse and nothing of interest). The adit the girl fell down is the only one I didn't go in, due to being unable to get up to it. There are a couple of others which go in a short way and further around Droskyn point, one which goes under the openwork and another which is totally unknown and goes into that big area of spoil with the venting capped shaft (minecap job).
The major adit goes into Perran St George, via Wheal East (which is the valley thing with lots of spoil and capped shafts) and about half way back through that adit, there is a left turn which takes you back under a lot of the Perranporth Mines, including Wheal Leisure (where it's only just under the surface). That's the biggun and the others are just trials, apart from the Droskyn Adit, which I am unaware of where the portal is (either near the waterwheel, or where the girl met her end)
NB:- Trying to get into the big adit is utterly bad news as it's in a massive sea cave which is only accessible for short periods during very low tides and involves a very exposed and hardcore cliff climb on vertical stuff. If there is even the slightest swell running, it will be a totally wet experience. (chest deep at the best of times)