TIME TO PICK THE IRONHEART SHIRAZ

View from my front veranda this morning: removing the veil from part of the Yangarra Ironheart vineyard, which is ready to pick ... the grapes taste utterly delicious. The juice is already unctuous and rich, the acid just beginning to decline, the pips  brittle and walnutty.

This vineyard is called Ironheart because it grows, somehow, in a few inches of aeolian (windblown) sand over solid slab ironstone, like this exposed bit (click to zoom):

Not to be confused with the covering aeolian sand, which is a very recent arrival, this is the Maslin Sand formation. It was washed here by freshwater from the mountains 40-56 million years ago. It's some of the final remnants of the ten-kilometre high mountain range which lived to the east across the Willunga Fault.  Weathered to the limit, these Maslin Sands underlie most of the McLaren Vale embayment, with varying layers of other sediments on the top.

This great range has almost completely eroded away, leaving what we call the South Mount Lofty Ranges. The central part of these is called the Adelaide Hills. That's them on the horizon.

You can see the weathered, eroded, rounded riverine quartzite gravels trapped in the sandstone. Fifteen kilometres away, at the coast, these sands are loose enough to dig with a shovel in the big Rocla pits at Maslin's Beach. These sands have been used to build Adelaide: they're the filler beneath its roads and the bedding below the foundations of its buildings. 

Up in this north-easternmost, elevated part of McLaren Vale, the sands have been exposed and oxidised. Washed for millenia in iron-rich water, they have become ironstone as the iron comes out of solution and cements the sand particles together. My little Ironheart Cottage is built from chunks of this, which may explain its magnetism. The Wirra Wirra winery is also built from this ironstone, quarried five hundred metres from here.

Here's a piece of Maslin Sand which has become partly ferruginised. In a way, ironstone grows. But as that epoch of washing in iron-rich water has long ceased, the process stopped, leaving fascinating examples like this:

Just to prove I took the top photograph, and indicate the great distances I have to travel to do my job, here's Milton Wordley's phone snap of your intrepid reporter hard at work: