PHUKET has many secrets. There are small, delightful beaches, inlets of great beauty, and Buddhist temples in sublime locations.

But perhaps the most unexpected secret of all lies in a valley at Ao Markham on Cape Panwa, on the island's east coast.

While the island has many self-styled boutique resorts in its modern incarnation as an international tourist paradise, there is only one boutique smelter.

Thaisarco, short for Thailand Smelting and Refining Co, Ltd, is the island's sole remaining functioning connection to the era when tin, not tourism, was the reason people came to Phuket.

Perhaps that makes this place sound historical and a part of the past: it isn't.

Thaisarco remains one of the world's top five tin smelting and refining companies, and the management is intent on maintaining its position as a pacesetter for adding value to quality products.

Phuket may have many secrets. But to wind down a country lane past a village to the Thaisarco smelter is to plunge into another world, a world of hard hats and safety boots and hot, flowing metal.

Australian Managing Director Michael Spratt and more than 230 Thai staff make this journey to another world every day.

By Mr Spratt's reckoning, the plant actually creates more than four times that number of jobs in Thailand. And the first thing he mentions to visitors is Thaisarco's contribution to the Phuket community.

''We've had a scholarship trust in place now for about 30 years,'' he says. ''It's provided educational assistance to a lot of kids here on Phuket.

''We raised some extra money after the tsunami that enabled us to support more scholarships post-2004, some in Phang Nga as well.

''There's also support for children's playgrounds, the schools and the mosques in villages close to the plant.''

Solder from Thaisarco mostly ends up in cameras, television sets, DVD players and the like.

''We're a very good quality producer,'' says Mr Spratt, who has been MD for six years. While hot metal is still poured at Thaisarco daily, the final outcome is very different now.

''The production of solder worldwide for electronic goods accounts for 52 to 54 percent of all the tin consumed,'' he says. ''That's a reversal from 30 or 40 years ago, when it was mostly about tin plate coating.''

Traditionally solder was 35 percent lead but today the more environmentally friendly varieties are 96-97 percent tin, with copper or alloys, and low-lead or no-lead, except in the US.

Thaisarco marks middle age, 45 years old on Phuket, this year.

''I think Thaisarco is on Phuket for two reasons,'' Mr Spratt says. ''Tin mining was huge in Thailand for a long time, as late as the very early 1980s, so there was an incentive to try to add value to all this tin.

''Secondly, HM The King paid a visit to Phuket in the early 60s and was staggered to see how much tin was being being mined. He remarked to his advisers thai it seemed an awfully good idea to try to add value to it, rather than simply shipping it all down to Malaysia or elsewhere.''

Union Carbide built the smelter, with Shell running it from the 1970s until 1995 when the tin industry was in decline and Amalgamated Metal Corporation took over.

''They managed to run a profit the first year that they owned it, and it has been profitable ever since,'' Mr Spratt says. ''Most of what we see now is the reprocessing of old tailings from Australia, Indonesia and Africa.''

Phuket production remains at about 20,000 tonnes a year and Thaisarco has gone down the path of value-adding to tin, producing lead-free solder, largely for the Asian market.

''We still have serious competition from Malaysia and emerging competition from China for concentrate,'' Mr Spratt says.

Some of the staff at Thaisarco boast a family history of parents or even grandparents who came from China to be a part of Phuket's early tin mining industry.

Vast expanses at Laguna Phuket, Blue Canyon and Loch Palm golf courses were clearly former tin mining sites, Mr Spratt says.

''In fact I rather suspect that most of these ponds that you see around the island that now form part of hotel complexes or reservoirs were all tin mining locations at one point or other.

''And of course, there was substantial dredging in-shore and off-shore in various forms, along Phuket and Phang Nga. There are still substantial reserves off-shore.''

Thaisarco is now adding value to tin, which has changed the nature of the traditional heavy metal industry to far more sophisticated processes that deliver almost totally lead-free products of different kinds.

Such is the secrecy of the trade that Phuketwan was asked not to photograph some of the processes.

But we can say, as the photo album shows better than words can explain, production of low-lead tin and solders is enhanced these days by highly sophisticated laboratory science.

And one of Phuket's living connections with a bygone era is now a whole lot less mysterious.