Yes VicGoldHunter, you can just go down a hole and have a go, and as long as you are careful it's perfectly safe.
I want to encourage people to go opal mining, opal prices are going up and there is still plenty of opportunity to hit it big. You do have to put in the effort, nothing comes easy.
To improve your chance of finding opal, spend time get to know the area you are going to prospect, you may notice something others have missed. The only indicator of success as an opal miner is how much effort you put in (and a bit(lot) of luck).
Firstly make sure you do not prospect on pegged claims, the mines department has maps of the registered claims on all the fields. At Lightning Ridge people who dig in other peoples mines are called Ratters, if you are caught then you may never be seen again! The newer fields are often pegged out, but old fields often have plenty of prospective ground available. The mines department frown on you prospecting or going down mines on unpegged ground, but as long as you sensible no one cares, opal miners do it all the time.
Start by spending time getting to know as much as you can about the existing opal fields, Google Earth is great way to see where opal was found. Most fields have only have few good claims, there is often a "run of opal" where opal lies along a structure such as a fault line or paleochannel. At Lighting Ridge the opal dirt is washed, the good claims have lot shafts with no dirt. At Coober Pedy and other fields the best opal was found where the piles of dirt are big. In Lightning Ridge shafts have to be back filled when you have finished working a claim. The exception is the older "preserved fields" these are the old opal fields between the 3 mile and 9 mile fields. Initially stick to these fields, there are lots of open shafts to explore and there is still a chance to find a pocket, or even a significant patch of opal. Since the eighties there have been 3 significant patches of opal found at Thorleys 6 mile and McDonalds 6 mile fields, these are two of the oldest fields in the Ridge, first mined a hundred years ago. These 3 patches conservatively produced over $500,000 worth of opal. There are similar stories from other fields.
When you find a opal field that you like, spend a lot of time understanding where the opal was found. Opal formation is controlled by faults, sometimes they can be seen from the surface, look for lines of trees or changes of vegetation. Spend a lot of time looking for pieces of potch and colour. A small piece of colour around an old shaft may be the lead you are looking for.
When you find an area that your interested in, get some ladders and go down and have a look.
Be warned, an opal mining can be dangerous, but if you are careful you will be OK.
When underground always wear a hard hat.
Before going down a shaft, make sure the collar of the shaft is secure, a rock falling a few meters can kill you.
Only use safe well made ladders well secured at the surface.
Mines are confined spaces, make sure the air is good. A naked flame will let you know if there is a shortage of oxygen, and if in doubt ventilate the mine before entering. Generally if a mine has multiple shafts there will be circulation and the air will be good. Be careful of blind shafts.
As you go down the shaft keep a look out for loose rocks in the wall.
As you approach the bottom of the shaft make sure there no new cracks in the shaft, a horizontal crack may mean the mine is about to collapse, you don't want to be the trigger.
When you get to the level, have a look around, extensive working and open spaces are unstable.
Old workings become dangerous as the ground dries out, cracks and becomes unstable.
Just because a mine has been propped does not mean it is safe.
Tunnels that are 1.5 meter wide or less should be OK, but ground varies. Keep an eye on the roof, sometimes rocks can fall out of the roof of a narrow drive.
Always be a bit of a chicken, if you are unsure stop, and get advice.
The opal level is easy to identify in Lightning Ridge, soft clay under a sandstone roof. Generally no sandstone means no opal, but never make assumptions. Opal is normally in the top couple of feet, but sometimes the opal is in the floor or the roof. There is often more than one level. Using a gouging pick, dig around looking for potch and colour, look near faults in the roof, slides in the opal dirt, bleached and iron stained opal dirt. Precious opal and potch form in similar places. Potch is important, but doesn't mean there is any opal in the area. If you spend enough time you will eventually get to identify where opal is likely to be.
When you find a claim to work, peg a claim and start digging, cost is about $1,000 including a $700 bond, and about $300 a year.
I have worked 2 claims in the Ridge. The first was in the eighties at Thorleys 6 mile, I found a patch beside the Danes patch from the seventies. The level had been split by a large flat slide, went down an exiting shaft to the west of the Danes. The roof was unsafe, I pulled down about 2 feet of opal dirt to a thin sandstone roof and found $30,000, just above an existing drive. I spent two and a half years mining and found about $90,000 worth of opal, I sold the claim and the new owners found another $35,000. I started mining with an auto hoist, electric jack hammer, and a gouging pick. You don't need much equipment to start.
Recently I've returned to the Ridge, my retirement scheme is digging holes. I've brought a house and setting up mining machinery, tandem tipper, agitator to wash dirt, blower, underground digger and auger drill, may take a while. I've pegged a claim at McDonalds 6 mile, not far from Thorleys where I worked in the eighties. A patch of opal was found at McDonalds in the nineties, beside it was an unworked claim with a old hand dug shaft, around the shaft was colour. Had a new shaft drilled, then drove towards the old shaft, found a slide with seam nobbies and good colour, no money yet but more trace. The claim is heavily faulted and a very good prospect.
As well as Coober Pedy and Lightning Ridge, another opal field worth considering is White Cliffs, not very active these days but has produced some brilliant crystal opal and there should plenty of good ground available.
Go and have a go at opal mining, but be warned opal fever is an incurable disease ;-)